Piezoelectric element and liquid ejection head

Abstract

Provided are a piezoelectric element having excellent displacement characteristics, and a liquid ejection head including the related piezoelectric element. The piezoelectric element has a piezoelectric layer comprising a plurality of layers and a pair of electrodes disposed so as to sandwich the piezoelectric layer, the piezoelectric layer comprising lead zirconate titanate, and the average value, the maximum value, and the minimum value of the hydrogen content in the plurality of layers in the center of the piezoelectric layer are H (Ave), H (max), and H (min), respectively, where H (Ave), H (max), and H (min) are the average value, the maximum value, and the minimum value of the hydrogen content in the plurality of layers in the center of the piezoelectric layer. When the larger one of the absolute values of (H (max)-H (ave)) / H (ave)) or (H (min)-H (ave)) / H (ave)) is set as [delta] H as the rate of change in the content of hydrogen, [delta] H is 24% or less.

Description

Technical Field

[0001] This invention relates to piezoelectric elements and liquid ejector heads. Background Technology

[0002] Previously, an image forming apparatus was proposed, which includes a liquid ejection head for ejecting liquids such as ink from a medium such as printing paper. As such a liquid ejection head, the following type of head is known: by using a piezoelectric element to vibrate a vibrating plate constituting the wall of a pressure chamber, liquid filling the pressure chamber is ejected from a nozzle.

[0003] The liquid ejector head described in Patent Document 1 has a piezoelectric element comprising a pair of electrodes and a piezoelectric layer sandwiched between the pair of electrodes. The piezoelectric layer has a perovskite structure such as PZT.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2010-214800

[0005] The piezoelectric layer described in Patent Document 1 is composed of multiple layers formed using a sol-gel method. Each layer of this multilayer is formed by sintering a gelled precursor film after coating and drying a coating solution containing an organic compound. By repeatedly performing the formation and sintering of the precursor film, a piezoelectric layer composed of multiple layers is formed.

[0006] In this piezoelectric element, it is known that compositional gradients exist between layers due to the crystallization temperature of the material. For example, in the case where the piezoelectric layer is lead zirconate titanate, titanium tends to segregate more at the boundaries where crystallization occurs earlier due to the difference in crystallization temperatures between lead titanate and lead zirconate. Therefore, in each layer, the composition sometimes differs near the boundary and at the center of the layer. If such compositional gradients occur, there is a concern that they may affect the displacement characteristics of the piezoelectric element.

[0007] Furthermore, through dedicated research, the inventors discovered that the displacement characteristics of piezoelectric elements vary depending on the hydrogen content of the piezoelectric layer. This occurs even in piezoelectric elements with equal compositional gradients. In particular, the inventors found that the rate of change of hydrogen content in the central layer of the piezoelectric layer affects the displacement characteristics of the piezoelectric element. Summary of the Invention

[0008] The preferred embodiment of the present invention relates to a piezoelectric element having a piezoelectric layer composed of multiple layers and a pair of electrodes disposed therebetween the piezoelectric layer, wherein the piezoelectric layer is made of lead zirconate titanate, and when the average value of the hydrogen content contained in the multiple layers in the center of the piezoelectric layer is defined as H(Ave), the maximum value is defined as H(max), and the minimum value is defined as H(min), and the larger of the absolute values ​​of (H(max)-H(ave)) / H(ave)) or (H(min)-H(ave)) / H(ave)) is defined as the rate of change of hydrogen content, ΔH is 24% or less.

[0009] The preferred embodiment of the present invention relates to a liquid ejector head having a piezoelectric element. Attached Figure Description

[0010] Figure 1 This is a schematic diagram illustrating the configuration of the image forming apparatus according to the first embodiment.

[0011] Figure 2 yes Figure 1 An exploded perspective view of the liquid ejector head shown.

[0012] Figure 3 yes Figure 1 A partial cross-sectional view of the liquid ejector head shown.

[0013] Figure 4 yes Figure 3 The cross-sectional view of the piezoelectric element shown.

[0014] Figure 5 yes Figure 3 The cross-sectional view of the piezoelectric element shown.

[0015] Figure 6 It is shown schematically. Figure 4 The diagram shows a piezoelectric element.

[0016] Figure 7 This is a table illustrating embodiments and comparative examples.

[0017] Figure 8 This is a graph showing the measurement results of the piezoelectric element of Example 1 by secondary ion mass spectrometry (SIMS).

[0018] Figure 9 This is a graph showing the measurement results of the piezoelectric element of Example 2 using a secondary ion mass spectrometer.

[0019] Figure 10 This is a graph showing the measurement results of the piezoelectric element of Comparative Example 1 by secondary ion mass spectrometry.

[0020] Figure 11This is a graph showing the measurement results of the piezoelectric element of Comparative Example 1 by secondary ion mass spectrometry.

[0021] Figure 12 It is shown Figure 6 A flowchart illustrating the manufacturing process of piezoelectric elements.

[0022] Figure 13 This is a schematic diagram showing the piezoelectric element of the first modified example.

[0023] Figure 14 This is a cross-sectional view of the piezoelectric element in the second variation.

[0024] Explanation of reference numerals in the attached figures

[0025] 3…liquid nozzle, 5…piezoelectric element, 6…protective film, 33…vibrating plate, 51…lower electrode, 52…upper electrode, 53…piezoelectric layer, 54…first hydrogen absorption layer (hydrogen absorption layer), 55…second hydrogen absorption layer, 100…image forming apparatus, 331…first vibrating body layer, 332…second vibrating body layer, 511…first electrode layer, 512…second electrode layer, 521…third electrode layer, 522…fourth electrode layer, 523…fifth electrode layer, 524…third hydrogen absorption layer (hydrogen absorption layer), 531…first layer, 532…second layer, 533…third layer, 534…fourth layer, 535…fifth layer, 536…sixth layer, A1…neutral shaft, C1…pressure chamber, N…nozzle. Detailed Implementation

[0026] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the dimensions or scales of the parts in the drawings may differ slightly from actual dimensions, and some parts are shown schematically for ease of understanding. Furthermore, unless otherwise specified in the following description, the scope of the invention is not limited to these embodiments. Additionally, "element β on element γ" means not limited to a configuration where element γ and element β are in direct contact, but also includes configurations where element γ and element β are not in direct contact. "Element γ and element β are equal" means that element γ and element β are substantially equal, including manufacturing tolerances, etc. Furthermore, "element α and element β are stacked" means that element α and element β can be arranged side-by-side in the vertical direction, without requiring element α and element β to be in direct contact.

[0027] 1. First Implementation Method

[0028] 1-1. Overall Structure of the Image Forming Apparatus 100

[0029] Figure 1This is a schematic diagram illustrating the configuration of the image forming apparatus 100 according to the first embodiment. Hereinafter, for ease of explanation, the X-axis, Y-axis, and Z-axis, which are orthogonal to each other, will be used appropriately in the description. Furthermore, one direction along the X-axis is referred to as the X1 direction, and the direction opposite to the X1 direction is referred to as the X2 direction. Similarly, one direction along the Y-axis is referred to as the Y1 direction, and the direction opposite to the Y1 direction is referred to as the Y2 direction. One direction along the Z-axis is referred to as the Z1 direction, and the direction opposite to the Z1 direction is referred to as the Z2 direction. The view along the Z-axis is referred to as a "top view." Additionally, the "stack direction" is the direction along the Z-axis. The Z-axis is generally a vertical axis. The Z2 direction is upward, and the Z1 direction is downward. However, the Z-axis may not be a vertical axis. Furthermore, the X-axis, Y-axis, and Z-axis are generally orthogonal to each other, but are not limited to this; for example, they may intersect at an angle within the range of 80° to 100°.

[0030] Figure 1 The image forming apparatus 100 is an inkjet printing apparatus that ejects ink, an example of a liquid, onto a medium 90. The medium 90 is typically printing paper, but any printing material such as resin film or fabric can be used as the medium 90. Figure 1 As illustrated, the image forming apparatus 100 is provided with a liquid container 9 for storing ink. For example, a box that can be detached from the image forming apparatus 100, an ink bag formed of a flexible film, or an ink can that can be refilled with ink can be used as the liquid container 9.

[0031] The image forming apparatus 100 includes a control unit 20, a media delivery mechanism 22, a moving mechanism 24, and a liquid ejection head 3. The control unit 20 includes, for example, one or more processing circuits such as a CPU (Central Processing Unit) or an FPGA (Field Programmable Gate Array) and one or more storage circuits such as a semiconductor memory, and controls all elements of the image forming apparatus 100 in a unified manner.

[0032] The media conveying mechanism 22 conveys the medium 90 along the Y-axis under the control of the control unit 20. Additionally, the moving mechanism 24, also under the control of the control unit 20, reciprocates the liquid nozzle 3 along the X-axis. The moving mechanism 24 includes a generally box-shaped conveyor body 242 that houses the liquid nozzle 3 and a conveyor belt 244 fixed to the conveyor body 242. It should be noted that a configuration in which multiple liquid nozzles 3 are mounted on the conveyor body 242, or a configuration in which the liquid container 9 is mounted together with the liquid nozzle 3 on the conveyor body 242, is also possible.

[0033] The liquid ejector head 3, under the control of the control unit 20, ejects ink supplied from the liquid container 9 from multiple nozzles onto the medium 90. Through the repeated back-and-forth movement of the liquid ejector head 3 and the medium conveying mechanism 22, ink is ejected onto the medium 90 in parallel, forming an image on the surface of the medium 90.

[0034] It should be noted that the image forming apparatus 100 is a serial head type in which the liquid ejector head 3 moves back and forth on the medium 90. However, the image forming apparatus 100 can also be a row head type in which the liquid ejector head 3 is fixed.

[0035] 1-2. Overall Structure of Liquid Ejector Head 3

[0036] Figure 2 yes Figure 1 An exploded perspective view of the liquid ejector head 3 shown. Figure 3 yes Figure 1 The diagram shows a partial cross-sectional view of the liquid ejector head, and is... Figure 2 A cross-sectional view of line aa in the diagram. Figure 3 The cross-section shown is parallel to the XZ plane. It should be noted that the Z-axis is the axis along the ink ejection direction of the liquid ejector head 3.

[0037] like Figure 2 As illustrated, the liquid nozzle 3 has a plurality of nozzles N arranged along the Y-axis. In the first embodiment, the plurality of nozzles N are divided into a first column La and a second column Lb arranged side-by-side with intervals between them along the X-axis. The first column La and the second column Lb are each a collection of a plurality of nozzles N arranged in a straight line along the Y-axis. The liquid nozzle 3 is a structure in which the elements associated with each nozzle N in the first column La and the elements associated with each nozzle N in the second column Lb are arranged approximately symmetrically. In the following description, the elements corresponding to the first column La will be described in detail, while the description of the elements corresponding to the second column Lb will be omitted as appropriate.

[0038] like Figure 2 as well as Figure 3 As illustrated, the liquid ejector head 3 includes a flow path forming substrate 31, a pressure chamber substrate 32, a vibrating plate 33, a nozzle plate 37, a vibration absorber 38, multiple piezoelectric elements 5, a sealing body 35, a housing portion 36, and a wiring substrate 40. The flow path forming substrate 31, pressure chamber substrate 32, vibrating plate 33, nozzle plate 37, vibration absorber 38, sealing body 35, and housing portion 36 are each a long, plate-shaped component along the Y-axis. Furthermore, the nozzle plate 37, flow path forming substrate 31, pressure chamber substrate 32, vibrating plate 33, and sealing body 35 are arranged side-by-side along the Z2 direction.

[0039] Nozzle plate 37 is a plate-shaped component having a plurality of nozzles N. Each of the plurality of nozzles N is a circular through-hole for ejecting ink. Nozzle plate 37 is bonded, for example, to the Z1 direction surface of flow path forming substrate 31 by an adhesive.

[0040] The flow path forming substrate 31 forms a flow path for ink flow. Specifically, the flow path forming substrate 31 has a space Ra, a relay liquid chamber Rb, a plurality of supply flow paths 312, and a plurality of connecting flow paths 314. The space Ra is an elongated opening formed along the Y-axis. The supply flow path 312 and the connecting flow path 314 are each through holes formed for each nozzle N. In a top view from the Z1 direction, each connecting flow path 314 overlaps with the corresponding nozzle N. The relay liquid chamber Rb is an elongated space formed along the Y-axis throughout the plurality of nozzles N, and connects the space Ra and the plurality of supply flow paths 312 to each other. A pressure chamber substrate 32 is bonded to the Z2 direction surface of the flow path forming substrate 31 using an adhesive.

[0041] Multiple pressure chambers C1 are formed on the pressure chamber substrate 32. Ink ejected from the nozzle N is stored in each pressure chamber C1. Each pressure chamber C1 is a space located between the nozzle plate 37 and the vibrating plate 33, formed through the inner wall surface 32a of the pressure chamber substrate 32. Each pressure chamber C1 is formed for each nozzle N. Each pressure chamber C1 is an elongated space extending along the X1 direction. Multiple pressure chambers C1 are arranged side-by-side along the Y-axis. Each pressure chamber C1 is connected to a connecting flow path 314 and a supply flow path 312. Therefore, each pressure chamber C1 is connected to the nozzle N via the connecting flow path 314, and to the space Ra via the supply flow path 312 and the relay liquid chamber Rb.

[0042] The nozzle plate 37, the flow path forming substrate 31, and the pressure chamber substrate 32 are manufactured, for example, by processing a single-crystal silicon (Si) substrate using semiconductor manufacturing techniques such as photolithography and etching. In the manufacture of the nozzle plate 37, the flow path forming substrate 31, and the pressure chamber substrate 32, any known materials and manufacturing methods can be used.

[0043] The surfaces of the vibrating plate 33 and the pressure chamber substrate 32 are connected opposite to those of the flow path forming substrate 31. The vibrating plate 33 is disposed on the pressure chamber C1 and is elastically deformable. The vibrating plate 33 is a rectangular plate-shaped component formed as a strip along the Y-axis when viewed from above. It should be noted that the vibrating plate 33 and the pressure chamber can be integrally formed or separately formed and joined by adhesives or the like.

[0044] A piezoelectric element 5 is formed on the surface of the vibrating plate 33 opposite to the pressure chamber C1. The piezoelectric element 5 is provided for each pressure chamber C1. Viewed from above, the piezoelectric element 5 is an elongated strip along the X-axis. The piezoelectric element 5 is a driving element that is driven by an applied driving signal, and applies pressure to the ink in the pressure chamber C1.

[0045] The sealing body 35 is bonded to the vibrating plate 33, for example, by an adhesive. The sealing body 35 is a structure that protects the multiple piezoelectric elements 5 and strengthens the mechanical strength of the pressure chamber substrate 32 and the vibrating plate 33. In the sealing body 35, a recess is formed on the surface opposite to the vibrating plate 33. The multiple piezoelectric elements 5 are accommodated inside the recess. In addition, the sealing body 35 has a space 353 for the wiring substrate 40 to be inserted.

[0046] The housing portion 36 is bonded to the flow path forming substrate 31, for example, by an adhesive. The housing portion 36 is a shell for storing ink supplied to multiple pressure chambers C1. The housing portion 36 is formed, for example, by injection molding of a resin material. A space Rc, a supply port 361, and a space 362 are formed in the housing portion 36. The supply port 361 is a conduit for supplying ink from the liquid container 9 and communicates with the space Rc. The space Rc communicates with the space Ra of the flow path forming substrate 31. The space formed by the space Rc and the space Ra functions as a liquid storage chamber R for storing ink supplied to multiple pressure chambers C1. The ink supplied from the liquid container 9 and passing through the supply port 361 is stored in the liquid storage chamber R. The ink stored in the liquid storage chamber R is supplied to multiple pressure chambers C1 in parallel from the relay liquid chamber Rb to each branch of the supply flow path 312. In addition, when viewed from above, the space 362 overlaps with the space 353 of the sealing body 35. Wiring substrate 40 is inserted in spaces 353 and 362.

[0047] The wiring substrate 40 is connected to the vibrating plate 33. The wiring substrate 40 is a mounting part with multiple wires formed thereon for electrically connecting the control unit 20 and the liquid ejector head 3. For example, a flexible substrate such as FPC (Flexible Printed Circuit) or FFC (Flexible Flat Cable) is preferably used in the wiring substrate 40. The drive signal for driving the piezoelectric element 5 and the reference voltage are supplied from the wiring substrate 40 to each piezoelectric element 5.

[0048] Additionally, the vibration absorber 38 is bonded to the Z1 direction surface of the flow path forming substrate 31, for example, by an adhesive. The vibration absorber 38 is a flexible thin film constituting the wall of the space Ra, and absorbs pressure fluctuations of the ink in the liquid storage chamber R.

[0049] In the liquid ejector head 3, if the piezoelectric element 5 flexes due to the application of voltage, the vibrating plate 33 will flex and vibrate in the direction that reduces the volume of the pressure chamber C1. As a result, the pressure in the pressure chamber C1 changes, and the ink in the pressure chamber C1 is ejected from the nozzle N. It should be noted that after the ink is ejected, the piezoelectric element 5 returns to its original position.

[0050] In addition, although the liquid ejector head 3 has Figure 3 The components shown are all of each element, but the components of the liquid nozzle 3 may not have all of each element, or may have additional elements.

[0051] 1-3. Piezoelectric element 5

[0052] Figure 4 as well as Figure 5 They are shown respectively Figure 3 A cross-sectional view of the piezoelectric element 5. Figure 4 The cross-section shown in the figure is parallel to the YZ plane. Figure 5 The cross-section shown in the figure is parallel to the XZ plane.

[0053] like Figure 4 as well as Figure 5 As shown, the piezoelectric element 5 mainly comprises a lower electrode 51, a piezoelectric layer 53, and an upper electrode 52. The lower electrode 51, the piezoelectric layer 53, and the upper electrode 52 are stacked in the stacking direction, i.e., along the Z-axis. Furthermore, as described later, as... Figure 6 As shown, the piezoelectric element 5 also has a first hydrogen absorption layer 54 and a second hydrogen absorption layer 55. It should be noted that the piezoelectric layer 53, the first hydrogen absorption layer 54, and the second hydrogen absorption layer 55 are sometimes collectively referred to as the intermediate layer 50 located between the lower electrode 51 and the upper electrode 52. Furthermore, as described later, the upper electrode 52 has a third hydrogen absorption layer 524. The first hydrogen absorption layer 54 and the third hydrogen absorption layer 524 are respectively equivalent to "hydrogen absorption layers".

[0054] like Figure 4 as well as Figure 5 As shown, the lower electrode 51 is positioned above the vibrating plate 33. The lower electrode 51 is a separate electrode for each piezoelectric element 5. A driving signal that varies voltage is applied to the lower electrode 51. The lower electrode 51 is elongated along the X-axis. Multiple lower electrodes 51 are spaced apart and arranged along the Y-axis. The lower electrode 51 contains a conductive material.

[0055] A piezoelectric layer 53 is disposed above the lower electrode 51. The piezoelectric layer 53 is, for example, a continuous strip-shaped dielectric film extending along the Y-axis and covering multiple piezoelectric elements 5. The piezoelectric layer 53 is, for example, a strip extending along the Y-axis and separated from the piezoelectric elements 5 by forming multiple notches. The piezoelectric layer 53 is, for example, composed of a perovskite-type composite oxide.

[0056] The upper electrode 52 is disposed above the piezoelectric layer 53. The upper electrode 52 is a strip-shaped common electrode that extends continuously along the Y-axis in a manner that covers multiple piezoelectric elements 5. A predetermined reference voltage is applied to the upper electrode 52. The upper electrode 52 contains a conductive material.

[0057] A voltage equivalent to the difference between the reference voltage applied to the upper electrode 52 and the drive signal corresponding to the ejection amount supplied to the lower electrode 51 is applied to the piezoelectric layer 53. The piezoelectric element 5 flexes and vibrates as the voltage is applied between the lower electrode 51 and the upper electrode 52.

[0058] The vibrating plate 33 vibrates by being driven by the piezoelectric element 5. In the illustrated example, the vibrating plate 33 is composed of a laminate including a first vibrating body layer 331 and a second vibrating body layer 332. The first vibrating body layer 331 is in contact with the pressure chamber substrate 32. The second vibrating body layer 332 is disposed above the first vibrating body layer 331. The first vibrating body layer 331 is formed of an elastic material such as silicon oxide (SiOx). The second vibrating body layer 332 is formed of an insulating material such as zirconium oxide (ZrOx). The first vibrating body layer 331 is formed, for example, by thermal oxidation of a portion of the pressure chamber substrate 32. The second vibrating body layer 332 is formed, for example, by a known film-forming technique such as sputtering. It should be noted that the vibrating plate 33 can be composed of one layer or more layers.

[0059] exist Figure 4 The diagram shows the neutral axis A1 of the vibrating plate 33. The neutral axis A1 refers to the position where the compressive force and the contractile force are balanced, and it is the position in the vibrating plate 33 where the stress along the axial direction of the XY plane is 0 (zero).

[0060] like Figure 5 As shown, two conductors 381 and 382 are disposed on the upper electrode 52. Conductors 381 and 382 are strip-shaped conductive films disposed along the edge of the upper electrode 52 in the X1 or X2 direction, respectively, and extending in the direction along the Y-axis. Conductors 381 and 382 are made of, for example, a low-resistance conductive material such as gold. Conductors 381 and 382 suppress voltage drop of the reference voltage in the upper electrode 52. In addition, conductors 381 and 382 also function as counterweights defining the vibration area of ​​the vibrating plate 33. It should be noted that conductors 381 and 382 can also be omitted.

[0061] Additionally, a connecting wire 380 is connected to one end of the lower electrode 51 along the long side direction of the X-axis. The lower electrode 51 is electrically connected to the wiring substrate 40 via the connecting wire 380. It should be noted that the upper electrode 52 is electrically connected to the aforementioned wiring substrate 40 via wiring, etc., which is omitted in the figure.

[0062] In addition, in this embodiment, the lower electrode 51 is a separate electrode and the upper electrode 52 is a common electrode, but it is also possible that the lower electrode 51 is a common electrode and the upper electrode 52 is a separate electrode.

[0063] Figure 6 It is shown schematically. Figure 4 The diagram shows the piezoelectric element 5. As previously described, the piezoelectric element 5 includes a lower electrode 51, a piezoelectric body layer 53, an upper electrode 52, a first hydrogen absorption layer 54, and a second hydrogen absorption layer 55. The lower electrode 51, the piezoelectric body layer 53, and the upper electrode 52 are each composed of multiple layers. In this embodiment, the first hydrogen absorption layer 54 is disposed between the lower electrode 51 and the piezoelectric body layer 53. The second hydrogen absorption layer 55 is disposed between the multiple layers constituting the piezoelectric body layer 53. The upper electrode 52 also has a third hydrogen absorption layer 524. The first hydrogen absorption layer 54 and the third hydrogen absorption layer 524 are respectively equivalent to "hydrogen absorption layers".

[0064] The lower electrode 51 has a first electrode layer 511 and a second electrode layer 512. The first electrode layer 511 is disposed above and in contact with the vibrating plate 33. The first electrode layer 511 contains, for example, platinum (Pt). The thickness of the first electrode layer 511 along the Z-axis is not particularly limited, but is, for example, 50 nm or more and 120 nm or less.

[0065] The second electrode layer 512 is disposed between and in contact with the first electrode layer 511 and the first hydrogen absorption layer 54. The second electrode layer 512 contains, for example, iridium (Ir). The thickness of the second electrode layer 512 along the Z-axis is not particularly limited, but is, for example, 5 nm or more and 50 nm or less. In this embodiment, the thickness of the second electrode layer 512 is thinner than the thickness of the first electrode layer 511, but it may also be thicker than the thickness of the first electrode layer 511.

[0066] It should be noted that in this embodiment, the lower electrode 51 is composed of two layers, but it can also be composed of one layer, or even three or more layers. In addition, the first electrode layer 511 and the second electrode layer 512 can be made of any conductive material, or they can be made of materials other than those mentioned above.

[0067] The first hydrogen absorption layer 54 is a "hydrogen absorption layer". The first hydrogen absorption layer 54 is disposed above the lower electrode 51 and between the lower electrode 51 and the piezoelectric layer 53 along the stacking direction of the piezoelectric element 5, i.e., the Z-axis. The first hydrogen absorption layer 54 has the function of absorbing hydrogen. According to the piezoelectric element 5 having the aforementioned first hydrogen absorption layer 54, it is able to absorb hydrogen present at the boundary between the lower electrode 51 and other layers, hydrogen present in the piezoelectric layer 53, or hydrogen that has the potential to enter the piezoelectric layer 53.

[0068] It should be pointed out that, in Figure 6 While the boundary between the first hydrogen absorption layer 54 and the piezoelectric layer 53 is clearly defined, it may not be. For example, a portion of the first hydrogen absorption layer 54 may be embedded in the piezoelectric layer 53, dispersed, or integrated. Furthermore, the composition within the first hydrogen absorption layer 54 may be fixed or tilted. Therefore, the composition may differ between the piezoelectric layer 53 side and the lower electrode 51 side of the first hydrogen absorption layer 54. Additionally, the thickness of the first hydrogen absorption layer 54 along the Z-axis is not particularly limited, but may be, for example, 2 nm or more and 20 nm or less. Furthermore, the first hydrogen absorption layer 54 may be constructed in multiple layers.

[0069] The piezoelectric layer 53 is a stack of layers consisting of a first layer 531, a second layer 532, a third layer 533, a fourth layer 534, a fifth layer 535, and a sixth layer 536 stacked sequentially. Furthermore, the piezoelectric layer 53 has a central layer 530. The central layer 530 is composed of multiple layers in the center of the piezoelectric layer 53. Specifically, the central layer 530 is composed of a third layer 533 and a fourth layer 534. It should be noted that the number of layers in the piezoelectric layer 53 is not limited to 6; it can be 5 or less, or 7 or more. By using a multi-layer structure instead of a single layer, a piezoelectric layer 53 with excellent piezoelectric properties can be formed.

[0070] The layers constituting the piezoelectric layer 53 are composed of perovskite-type composite oxides. More specifically, the layers are composed of lead zirconate titanate (PZT:Pb(Zr,Ti)O3).

[0071] In addition, the thickness of each layer of the piezoelectric layer 53 is not particularly limited, but for example, it is 90 nm or more and 250 nm or less.

[0072] The first layer 531 is disposed between and in contact with the first hydrogen absorption layer 54 and the second hydrogen absorption layer 55. The second hydrogen absorption layer 55 is disposed between and in contact with the first layer 531 and the second layer 532.

[0073] The second hydrogen absorption layer 55 has the function of absorbing hydrogen present in the layers or between the layers constituting the piezoelectric element 5. In particular, the second hydrogen absorption layer 55 preferably absorbs hydrogen in the first layer 531 and the second layer 532.

[0074] It should be pointed out that, in Figure 6 In this embodiment, although the boundaries of the second hydrogen absorption layer 55 and the second layer 532, as well as the boundaries of the second hydrogen absorption layer 55 and the first layer 531, are clearly described, they may not be clearly defined. For example, a portion of the second hydrogen absorption layer 55 may be embedded in the first layer 531 or the second layer 532, or it may be dispersed, or it may be integral. Furthermore, the composition within the second hydrogen absorption layer 55 may be fixed or tilted. Therefore, the composition may differ between the second layer 532 side and the first layer 531 side of the second hydrogen absorption layer 55. Additionally, the thickness of the second hydrogen absorption layer 55 along the Z-axis is not particularly limited, but may be, for example, 2 nm or more and 20 nm or less. Furthermore, in this embodiment, the film thickness D5 of the second hydrogen absorption layer 55 is thinner than the film thickness D4 of the first hydrogen absorption layer 54, but it may also be greater than or equal to the film thickness D4 of the first hydrogen absorption layer 54. Furthermore, the second hydrogen absorption layer 55 may be composed of multiple layers.

[0075] The upper electrode 52 is a structure in which a third electrode layer 521, a fourth electrode layer 522, a fifth electrode layer 523, and a third hydrogen absorption layer 524 are stacked sequentially. The third electrode layer 521 is disposed above the piezoelectric layer 53 and is in contact with the sixth layer 536 of the piezoelectric layer 53. The third electrode layer 521 contains, for example, iridium oxide (IrOx). The thickness of the third electrode layer 521 along the Z-axis is not particularly limited, but is, for example, 5 nm or more and 20 nm or less. The fourth electrode layer 522 contains, for example, titanium oxide (TiOx). The thickness of the fourth electrode layer 522 along the Z-axis is not particularly limited, but is, for example, 2 nm or more and 20 nm or less. The fifth electrode layer 523 contains, for example, iridium (Ir). The thickness of the fifth electrode layer 523 along the Z-axis is not particularly limited, but is, for example, 5 nm or more and 50 nm or less.

[0076] The third hydrogen absorption layer 524 is a "hydrogen absorption layer". The third hydrogen absorption layer 524 is disposed on the upper electrode 52 side relative to the piezoelectric layer 53, and is the uppermost layer of the upper electrode 52. The third hydrogen absorption layer 524 has the function of absorbing hydrogen. By providing the aforementioned third hydrogen absorption layer 524, compared to the case where it is not provided, it is possible to suppress hydrogen from entering the piezoelectric layer 53 from the upper electrode 52 side. Furthermore, it is possible to reduce the hydrogen content of each of the third electrode layers 521 to the fifth electrode layers 523.

[0077] The thickness of the third hydrogen absorption layer 524 along the Z-axis is not particularly limited, but is, for example, 5 nm or more and 20 nm or less. The third hydrogen absorption layer 524 has the function of absorbing hydrogen present in the layers or between the layers constituting the piezoelectric element 5. In particular, the third hydrogen absorption layer 524 preferably absorbs hydrogen from the upper electrode 52. It should be noted that the composition within the third hydrogen absorption layer 524 can be constant or tilted. Furthermore, they can also be formed in multiple layers.

[0078] It should be pointed out that, in Figure 6 In this example, no orientation control layer for controlling the orientation of the piezoelectric layer 53 is provided between the first hydrogen absorption layer 54 and the piezoelectric layer 53, but such an orientation control layer may be provided. Alternatively, the first hydrogen absorption layer 54 may also function as such an orientation control layer. Since the first hydrogen absorption layer 54 functions as such an orientation control layer, there is no need to provide a separate orientation control layer, thus simplifying manufacturing. It should be noted that the orientation control layer may, for example, preferentially orient the crystals in the upper layers toward a predetermined planar orientation, or adjust the degree of orientation of the predetermined planar orientation.

[0079] Similarly, although no orientation control layer for controlling the orientation of the second layer 532 is provided between the second hydrogen absorption layer 55 and the second layer 532, such a configuration control layer may still be provided. The second hydrogen absorption layer 55 may also have the function of such an orientation control layer. Since the second hydrogen absorption layer 55 has the function of such an orientation control layer, it is not necessary to provide a separate orientation control layer, thus making manufacturing easy.

[0080] 1-4. Piezoelectric layer

[0081] As previously described, the piezoelectric layer 53 is composed of multiple layers. The piezoelectric layer 53 is disposed between a pair of electrodes, namely a lower electrode 51 and an upper electrode 52. The multiple layers constituting the piezoelectric layer 53 have a central layer 530, which corresponds to a "central multilayer". In this embodiment, the central layer 530 is the third layer 533, the fourth layer 534, and the fifth layer 535. The central layer 530 is located at the center and adjacent to the center of the piezoelectric layer 53, and is not in contact with the upper electrode 52, the lower electrode 51, or the second hydrogen absorption layer 55 located above and below the piezoelectric layer 53; it is sandwiched between the other layers of the piezoelectric layer 53. Therefore, the central layer 530 does not contact any layers in the piezoelectric layer 53 other than those constituting the piezoelectric layer 53. Furthermore, the multiple layers constituting the piezoelectric layer 53 have a "central layer". In this embodiment, the "central layer" is the third layer 533, the fourth layer 534, or the fifth layer 535. Furthermore, "the central layer" refers to a layer in the central layer 530 that is not in contact with the upper electrode 52, the lower electrode 51, and the second hydrogen absorption layer 55 located above and below the piezoelectric layer 53. The following explanation will focus on the case where "the central layer" is the third layer 533.

[0082] The rate of change ΔH of the hydrogen content in the central layer 530 of the piezoelectric layer 53 is less than 24%.

[0083] The rate of change ΔH is the larger of the absolute values ​​of (H(max) - H(ave)) / H(ave)) or (H(min) - H(ave)) / H(ave)).

[0084] H(Ave) is the average hydrogen content in the third layer 533. H(max) is the maximum hydrogen content in the third layer 533. H(min) is the minimum hydrogen content in the third layer 533. H(Ave), H(max), and H(min) are determined, for example, by secondary ion mass spectrometry.

[0085] The rate of change of hydrogen content ΔH in the central layer 530 is less than 24%, which, compared to the case where ΔH exceeds 24%, can suppress the decrease in displacement characteristics of the piezoelectric element 5.

[0086] The hysteresis characteristics of the piezoelectric element 5 change over time due to the hydrogen content of the piezoelectric layer 53, and vary significantly from the design stage. As a result, the displacement characteristics of the piezoelectric element 5 decrease over time. Furthermore, the displacement amount obtained based on the driving voltage value set during the design stage changes. This decrease in displacement characteristics is significant when the piezoelectric layer 53 is formed from multiple layers. As described later, the piezoelectric layer 53 is formed by repeatedly performing multiple layers of film deposition and sintering. During this manufacturing process, it is believed that the hydrogen content of the piezoelectric layer 53 changes due to the infiltration of hydrogen into it. Therefore, when comparing multiple piezoelectric elements 5, even when the compositional gradient in the piezoelectric layer 53 is generated in the same manner, a decrease in the displacement characteristics of the piezoelectric element 5 due to the hydrogen content can be observed.

[0087] Through in-depth research, the inventors discovered that by suppressing the rate of change ΔH of the hydrogen content in the central layer 530 of the piezoelectric layer 53, the decrease in the displacement characteristics of the piezoelectric element 5 over time can be suppressed. Specifically, by keeping the rate of change ΔH below 21%, the decrease in the displacement characteristics of the piezoelectric element 5 can be suppressed. Furthermore, since the decrease in the displacement characteristics of the piezoelectric element 5 from the design stage is suppressed, it is not necessary to redesign the driving voltage or waveform to match the change over time and adjust for the difference, thus improving ease of use.

[0088] The central layer 530 in the piezoelectric layer 53 has a significant impact on the displacement characteristics of the piezoelectric element 5. For example, it is believed that the larger the extent of the layer farther from the neutral axis A1 of the piezoelectric layer 53, the higher the performance of the piezoelectric element 5, which has an impact. It is believed that by suppressing the rate of change ΔH of the hydrogen content in the central layer 530, the rate of change of the hydrogen content in other layers, and thus the average hydrogen content in the piezoelectric layer 53, can be reduced.

[0089] Furthermore, since the central layer 530 is not in contact with the upper electrode 52, the lower electrode 51, or the second hydrogen absorption layer 55, and is sandwiched between other layers of the piezoelectric layer 53, the influence from the upper electrode 52, the lower electrode 51, and the second hydrogen absorption layer 55 can be suppressed to determine the hydrogen content. For example, when measuring a layer in contact with the upper electrode 52 or the lower electrode 51 using secondary ion mass spectrometry, the measurement may sometimes be unstable due to the influence of the boundary between the upper electrode 52 or the lower electrode 51 and the layer. That is, the secondary ion intensity near the boundary may sometimes change significantly due to the boundary effect. If the central layer, which is not in contact with the upper electrode 52 and the lower electrode 51, is measured, the influence from the upper electrode 52 and the lower electrode 51 can be suppressed to determine the hydrogen content.

[0090] By ensuring that the rate of change of hydrogen content ΔH in the central layer 530 is below 21%, the increase in displacement difference among the multiple piezoelectric elements 5 can be suppressed. Therefore, the effort required to redesign the drive voltage and waveform for each piezoelectric element 5 to adjust the displacement difference between the multiple piezoelectric elements 5 can be eliminated. This improves the ease of use of the piezoelectric elements 5.

[0091] Furthermore, while the aforementioned rate of change of hydrogen content ΔH is acceptable as long as it is 24% or less, it is preferably 20% or less. By keeping the rate of change ΔH below 20%, the decrease in the displacement characteristics of the piezoelectric element 5 can be suppressed compared to cases where it exceeds 20%.

[0092] Furthermore, in the central layer 530, it is preferable that the average hydrogen content of the layer below in the stacking direction, namely the third layer 533, is lower than the average hydrogen content of the layers above, namely the fourth layer 534 and the fifth layer 535. It is believed that by having the hydrogen content of the third layer 533 lower than that of the fourth layer 534 and the fifth layer 535, the hydrogen content of each of the first hydrogen absorption layers 54 and 55 can be reduced through the first hydrogen absorption layer 54 and the second hydrogen absorption layer 55. It is believed that by reducing the hydrogen content of the lower layers in the piezoelectric layer 53, the entry and diffusion of hydrogen from the upper layers can be reduced during the manufacturing of the piezoelectric layer 53. Therefore, by having the hydrogen content of the third layer 533 lower than that of the fourth layer 534 and the fifth layer 535, the overall hydrogen content of the piezoelectric layer 53 can be reduced. Therefore, the displacement characteristics of the piezoelectric element 5 can be improved. It should be noted that the hydrogen content of the fourth layer 534 is preferably less than that of the fifth layer 535. Furthermore, the hydrogen content of each layer is determined, for example, using secondary ion mass spectrometry, and the average hydrogen content is calculated by averaging the hydrogen content of the layers.

[0093] Furthermore, in the third layer 533 within the central layer 530, it is preferable that the hydrogen content on the lower side of the stacking direction is greater than the hydrogen content on the upper side. In other words, in the third layer 533, the hydrogen content is low at locations far from the neutral axis A1 of the piezoelectric layer 53. Therefore, the decrease in the displacement characteristics of the piezoelectric element 5 can be suppressed. The lower side of the layer refers to the portion of the layer located in the Z1 direction. For example, it refers to the range from the lower surface of the layer in the Z1 direction towards the Z2 direction up to 25 nm. Similarly, the upper side of the layer refers to the portion of the layer located in the Z2 direction. For example, it refers to the range from the upper surface of the layer in the Z2 direction towards the Z1 direction up to 25 nm. The hydrogen content within this range is determined, for example, using secondary ion mass spectrometry.

[0094] It should be noted that, in the fourth layer 534 and the fifth layer 535, it is also preferable that the hydrogen content on the lower side of the stacking direction is greater than the hydrogen content on the upper side.

[0095] Furthermore, while the film thickness of each layer of the central layer 530 in the piezoelectric layer 53 is not particularly limited, it is preferably 100 nm or more and 300 nm or less. For example, the film thickness D3 of the third layer 533 is not particularly limited, but is preferably 100 nm or more and 300 nm or less.

[0096] As described later, the manufacturing process of the piezoelectric layer 53 sometimes includes a debinding process and a sintering process. In this case, there is a possibility that hydrogen in the precursors constituting each layer of the piezoelectric layer 53 may not be completely removed during the debinding process, or that hydrogen may enter the piezoelectric layer 53 during the sintering process. In particular, the possibility of incomplete hydrogen removal is high when the piezoelectric layer 53 is formed using a sol-gel method. By having a film thickness D3 of 100 nm or more and 300 nm or less, hydrogen can be more easily removed during the debinding process compared to cases outside this range, and hydrogen entry is made more difficult by shortening the sintering process time.

[0097] Similarly, the film thickness D3 of the third layer 533, the film thickness D4 of the fourth layer 534, and the film thickness D5 of the fifth layer, which are the central layers constituting the piezoelectric layer 53, are not particularly limited, but are preferably 100 nm or more and 300 nm or less.

[0098] Furthermore, when the piezoelectric layer 53 is composed of a perovskite-type composite oxide containing Ti, the rate of change of titanium content ΔTi in the central layer 530 is preferably 14% or less.

[0099] The rate of change ΔTi is the larger of the absolute values ​​of (Ti(max) - Ti(ave)) / Ti(ave)) or (Ti(min) - Ti(ave)) / Ti(ave)).

[0100] Ti(Ave) is the average titanium content in the central layer 530. Ti(max) is the maximum titanium content in the central layer 530. Ti(min) is the minimum titanium content in the central layer 530. Ti(Ave), Ti(max), and Ti(min) are determined, for example, by secondary ion mass spectrometry.

[0101] The compositional gradient of titanium in the piezoelectric layer 53 affects the displacement characteristics of the piezoelectric element 5. Since the rate of change ΔTi through the central layer 530 of the piezoelectric layer 53 is less than 14%, the compositional gradient of titanium in the piezoelectric layer 53 is suppressed compared to cases exceeding 14%, thus preventing a decrease in displacement characteristics. Furthermore, titanium has a high hydrogen storage capacity. Therefore, a large deviation in titanium content leads to a large deviation in hydrogen content in the piezoelectric layer 53. Thus, by suppressing the deviation in titanium content, the deviation in hydrogen content can be suppressed. Therefore, displacement characteristics can be improved.

[0102] The first hydrogen absorption layer 54 and the third hydrogen absorption layer 524 are respectively equivalent to "hydrogen absorption layers". The first hydrogen absorption layer 54 and the third hydrogen absorption layer 524 are disposed in the stacking direction of the multiple layers constituting the piezoelectric layer 53, sandwiching the piezoelectric layer 53. The piezoelectric layer 53 is disposed between the first hydrogen absorption layer 54 and the third hydrogen absorption layer 524.

[0103] The amount of hydrogen in the piezoelectric layer 53 increases due to its generation during the degreasing and sintering of the precursor and its entry from the outside of the piezoelectric element 5. By providing the first hydrogen absorption layer 54 and the third hydrogen absorption layer 524, the hydrogen content in the piezoelectric layer 53 can be reduced compared to the case where they are not provided.

[0104] Furthermore, in this embodiment, a second hydrogen absorption layer 55 is provided. Therefore, the hydrogen content of the piezoelectric layer 53 can be further reduced.

[0105] The first hydrogen absorption layer 54 is made of a material capable of absorbing hydrogen. Specifically, the first hydrogen absorption layer 54 includes a hydrogen storage material that can combine with hydrogen to form a hydride. The hydrogen storage material absorbs or releases hydrogen through temperature or pressure. During hydrogen absorption in the first hydrogen absorption layer 54, hydrogen invades the interstices in the crystal lattice of the hydrogen storage material. The hydrogen storage material includes metals such as magnesium (Mg), vanadium (V), lanthanum (La), and titanium (Ti), alloys or compounds containing these metals. The first hydrogen absorption layer 54 is, for example, made of titanium or lead titanate (PbTiO3). Alternatively, the first hydrogen absorption layer 54 is, for example, made of a composite oxide containing bismuth (Bi), iron (Fe), titanium (Ti), and lead (Pb).

[0106] In addition, the second hydrogen absorption layer 55 and the third hydrogen absorption layer 524 also contain hydrogen storage materials that can combine with hydrogen to form hydrides.

[0107] Furthermore, as mentioned earlier, the piezoelectric layer 53 is composed of a perovskite-type composite oxide, namely lead zirconate titanate (PZT). By using PZT for the piezoelectric layer 53, the effect of suppressing changes in the hysteresis characteristics of the piezoelectric element 5 through the provision of the first hydrogen absorption layer 54 can be particularly significant. Moreover, when the piezoelectric layer 53 is composed of multiple layers, the effect of providing the first hydrogen absorption layer 54 can be particularly significant.

[0108] Furthermore, it is particularly preferred that the first hydrogen absorption layer 54, the second hydrogen absorption layer 55, and the third hydrogen absorption layer 524 each contain titanium. Moreover, it is preferable that these layers are each composed of titanium. Titanium has excellent hydrogen absorption properties. Therefore, by including titanium in these layers, more hydrogen that could potentially enter the piezoelectric layer 53 can be absorbed compared to the case where it is not included.

[0109] Figure 7 This is a table illustrating embodiments and comparative examples. Figure 7 Examples 1-10 and Comparative Examples 1-6 are shown in the table. Examples 1-10 and Comparative Examples 1-6 have a 6-layer piezoelectric layer 53. The thickness of each layer of the piezoelectric layer 53 is approximately 220 nm. Figure 7 The results and evaluations show the hydrogen content, change rate ΔTi, and ΔH in the central layer 530 determined and calculated by secondary ion mass spectrometry.

[0110] Each piezoelectric layer 53 in Examples 1-10 is composed of a Ti-containing perovskite-type composite oxide, namely lead zirconate titanate. Furthermore, the hydrogen content and concentration in the central layer 530 of Examples 1-10 and Comparative Examples 1-6 differ. The hydrogen concentration in the central layer 530 was adjusted by varying the heating conditions in the manufacturing process and the amount of hydrogen in the hydrogen absorption layer. Besides... Figure 7 The illustrated embodiments Figure 6 In addition to the configuration of the piezoelectric element 5 shown, examples of configurations shown in the following modified examples are also included. The first modified example described later corresponds to Embodiment 9, and the second modified example described later corresponds to Embodiment 10.

[0111] like Figure 7 As shown, in Examples 1-10, the larger of the absolute values ​​of either (H(max) - H(ave)) / H(ave)) or (H(min) - H(ave)) / H(ave)) of the rate of change of hydrogen content ΔH in the central layer 530 is 24% or less. On the other hand, in Comparative Examples 1-6, the larger of the absolute values ​​of either (H(max) - H(ave)) / H(ave)) or (H(min) - H(ave)) / H(ave)) of the rate of change of hydrogen content ΔH in the third layer 533 exceeds 24%.

[0112] Compared with the comparative examples, each embodiment exhibits superior displacement characteristics. The rate of displacement change over time was evaluated based on the piezoelectric element 5. A durability test was conducted to determine the rate of displacement decrease of the piezoelectric element 5 over time before and after the application of a predetermined driving pulse. This durability test involved continuously applying 10 billion predetermined driving pulses to a liquid nozzle equipped with the piezoelectric element 5. The predetermined driving pulse was a trapezoidal waveform with a voltage of 25V and a frequency of 100Hz. An evaluation of "0" indicates a rate of displacement change over time of less than -5.0%. An evaluation of "◎" indicates a rate of change over time of less than -3.0%.

[0113] In Examples 1-10, the ΔH is less than 24%, while in Comparative Examples 1-6 it exceeds 24%. Therefore, compared to the Comparative Examples, the displacement change rate of the piezoelectric element 5 over time is lower in each Example. Thus, compared to Comparative Examples 1-6, Examples 1-10 can suppress the decrease in the displacement characteristics of the piezoelectric element 5. Therefore, the liquid ejector head equipped with the piezoelectric element 5 of Examples 1-10 can exhibit and maintain excellent ejection characteristics.

[0114] Furthermore, in Examples 1, 2, 5, 7-10, the rate of change ΔH of the hydrogen content in the central layer 530 is less than 20%. The rate of change over time in Examples 1, 2, 5, 7-10 is less than -3.0%, which is extremely small. Therefore, compared with other examples, Examples 1, 2, 5, 7-10 can suppress the decrease in the displacement characteristics of the piezoelectric element 5. Therefore, the liquid ejector head equipped with the piezoelectric element 5 of Examples 1, 2, 5, 7-10 can exhibit and maintain particularly excellent ejection characteristics.

[0115] Furthermore, in Examples 1-10, the rate of change ΔTi of titanium content in the central layer 530 was less than 14%. Additionally, although in Figure 7 Not shown in the figure, but the film thickness of each layer of the central layer 530 is approximately 220 nm. In addition, the piezoelectric element 5 of Examples 1 to 10 has a first hydrogen absorption layer 54, a second hydrogen absorption layer 55 and a third hydrogen absorption layer 524.

[0116] Figure 8 This is a graph showing the measurement results of the piezoelectric element 5 of Example 1 using a secondary ion mass spectrometer (SIMS). Figure 9 This is a graph showing the measurement results of the piezoelectric element 5 of Example 2 using a secondary ion mass spectrometer. Figure 10 This is a graph showing the measurement results of the piezoelectric element 5 of Comparative Example 1 using a secondary ion mass spectrometer. Figure 11 This is a graph showing the measurement results of the piezoelectric element 5 of Comparative Example 2 using a secondary ion mass spectrometer.

[0117] It should be noted that in Examples 1 and 2, and Comparative Examples 1 and 2, the material of the first electrode layer 511 is platinum, and the material of the second electrode layer 512 is iridium. The first hydrogen absorption layer 54 contains titanium. The second hydrogen absorption layer 55 contains titanium. The material of the third electrode layer 521 is iridium oxide, the material of the fourth electrode layer 522 is titanium oxide, the material of the fifth electrode layer 523 is iridium, and the material of the third hydrogen absorption layer 524 is titanium.

[0118] Figures 8-11 The horizontal axis represents depth [nm]. Since the analysis is performed from the upper electrode 52 towards Z1, the side with shallower depth is the upper electrode 52 side, and the side with deeper depth is the lower electrode 51 side. Figures 8-11 The vertical axis represents the concentration of hydrogen [atoms / cc]. This hydrogen concentration is quantified using standard samples doped with a known concentration of the target element. It should be noted that for titanium and zirconium, it is expressed as ionic strength. It should also be noted that "E" represents a power of 10. For example, 1E+20 represents 1 × 10²⁰, and 1E+19 represents 1 × 10¹⁹.

[0119] In addition, Figures 8-11 Although clear line segments are drawn along the boundaries of each layer, the positions of the boundaries may deviate slightly depending on the content being judged. Furthermore, due to measurement errors in SIMS, boundary effects, etc., the peak positions may sometimes fluctuate relative to the depths of the first hydrogen absorption layer 54 and the second hydrogen absorption layer 55. In such cases, hydrogen peaks observed near the depths of the first and second hydrogen absorption layers 54 and 55 are considered as peak values ​​within the first and second hydrogen absorption layers 54 and 55, respectively.

[0120] exist Figures 8-11 The values ​​in the table represent H(max), H(min), Ti(max), and Ti(min). Figure 8 The first embodiment and Figure 9 The second embodiment is respectively with Figure 10 The first comparative example and Figure 11 Compared to the second comparative example, the rate of change ΔH of hydrogen content in the central layer 530 is smaller. Additionally, Figure 8 The first embodiment and Figure 9 The second embodiment is respectively with Figure 10 The first comparative example and Figure 11 Compared to the second comparative example, the rate of change ΔTi of titanium content in the central layer 530 is smaller. It should be noted that... Figures 8-11 In this context, Ti is expressed as a second ionic strength.

[0121] It should be noted that the H (Ave) and Ti (Ave) of the central layer 530 are calculated by averaging the hydrogen content and titanium content from one end boundary of the central layer to the other end boundary.

[0122] In addition, Figure 8 In the first embodiment, the average hydrogen content of the third layer 533 is less than the average hydrogen content of the fourth layer 534 and the average hydrogen content of the fifth layer 535. Furthermore, the average hydrogen content of the fourth layer 534 is less than the average hydrogen content of the fifth layer 535.

[0123] 1-5. Manufacturing method of piezoelectric element 5

[0124] Figure 12 It is shown Figure 6 A flowchart illustrating the manufacturing method of the piezoelectric element 5. (See attached diagram.) Figure 12 As shown, the manufacturing method of the piezoelectric element 5 includes a lower electrode forming step S11, an intermediate layer forming step S12, and an upper electrode forming step S13. These steps are performed sequentially.

[0125] In the lower electrode formation step S11, a lower electrode 51 is formed. The lower electrode formation step S11 includes the formation of a first electrode layer 511 and the formation of a second electrode layer 512. Specifically, firstly, for example, a layer containing a conductive material such as platinum is deposited on a vibrating plate 33 by sputtering, vapor deposition, or CVD (Chemical Vapor Deposition) to form a film, thereby forming the first electrode layer 511. Next, for example, a layer containing a conductive material such as iridium is deposited on the first electrode layer 511 by sputtering, vapor deposition, or CVD to form a film, thereby forming the second electrode layer 512.

[0126] The intermediate layer formation process S12 includes the formation of a first hydrogen absorption layer 54, a piezoelectric layer 53, and a second hydrogen absorption layer 55. Specifically, firstly, a layer containing a hydrogen storage material such as titanium is formed on the lower electrode 51 using sputtering, vapor deposition, or CVD. Next, a first-layer precursor composed of a perovskite-type composite oxide such as PZT is formed and degreased on the layer containing the hydrogen storage material using a sol-gel method. Then, the layer containing the hydrogen storage material and the first-layer precursor are sintered. As a result, the first hydrogen absorption layer 54 and the first layer 531 are formed.

[0127] Next, a film containing a hydrogen storage material such as titanium is formed on the first layer 531 using sputtering, vapor deposition, or CVD. Then, a second layer precursor composed of a perovskite-type composite oxide such as PZT is formed and degreased on the other layers containing the hydrogen storage material using a sol-gel method. Next, the other layers containing the hydrogen storage material and the second layer precursor are sintered. As a result, a second hydrogen absorption layer 55 and a second layer 532 are formed.

[0128] When forming the second hydrogen absorber layer 55, it is possible that moisture remains on the surface of the first layer 531. Therefore, it is preferable to perform a heating process to remove surface moisture during the formation of the second hydrogen absorber layer 55. This reduces the amount of moisture remaining on the surface of the first layer 531. Consequently, the amount of hydrogen absorbed by the second hydrogen absorber layer 55 can be reduced during its formation, allowing for sufficient hydrogen absorption by the formed second hydrogen absorber layer 55.

[0129] Next, after forming a third-layer precursor composed of perovskite-type composite oxides such as PZT using the sol-gel method on the second layer 532, the third-layer precursor is sintered. This forms the third layer 533. The fourth layer 534, fifth layer 535, and sixth layer 536 are formed using the same method. Next, after the formation of the sixth layer 536, the first hydrogen absorption layer 54, the second hydrogen absorption layer 55, and the piezoelectric layer 53 are sintered together.

[0130] When each layer of the piezoelectric layer 53 is formed using the sol-gel method, the shape and crystallinity of the lower layer can affect the shape and crystallinity of the upper layer. In this embodiment, the hydrogen content of the second layer 532 is lower than that of the third layer 533. Therefore, it is possible to suppress the influence of the shape and crystallinity of the second layer 532 on the third layer 533 during the stage of forming a film on the middle layer portion of the piezoelectric layer 53 using the sol-gel method.

[0131] In the upper electrode formation process S13, an upper electrode 52 is formed. The upper electrode formation process S13 includes the formation of a third electrode layer 521, a fourth electrode layer 522, a fifth electrode layer 523, and a third hydrogen absorption layer 524. Specifically, for example, after a layer containing a conductive material such as iridium is deposited on the sixth layer 536 using sputtering, vapor deposition, or CVD, a third electrode layer 521 containing a metal oxide or the like is formed by sintering. Next, after a layer containing a conductive material such as titanium is deposited on the third electrode layer 521 using sputtering, vapor deposition, or CVD, a fourth electrode layer 522 containing a metal oxide or the like is formed by sintering.

[0132] Next, a fifth electrode layer 523 is formed by depositing a layer containing a conductive material such as iridium on the fourth electrode layer 522 using sputtering, evaporation, or CVD. Next, a third hydrogen absorption layer 524 is formed by depositing a layer containing a hydrogen storage material such as titanium on the fifth electrode layer 523 using sputtering, evaporation, or CVD. As described above, the piezoelectric element 5 is manufactured.

[0133] 2. Variations

[0134] The embodiments illustrated above can be modified in many ways. Specific modifications that can be applied to the foregoing embodiments are illustrated below. Two or more methods selected arbitrarily from the following examples can be appropriately combined without contradiction.

[0135] 2-1. First Variation Example

[0136] Figure 13 This is a schematic diagram showing the piezoelectric element 5A of the first modified example. (See diagram for example.) Figure 13 As shown, the first hydrogen absorption layer 54A of the piezoelectric element 5A in the first modified example is composed of multiple layers with different main constituent materials. Specifically, the first hydrogen absorption layer 54A includes a first absorption layer 541 and a second absorption layer 542. The second absorption layer 542 is mainly composed of a material different from the main constituent material of the first absorption layer 541. The first absorption layer 541 is, for example, made of titanium. The second absorption layer 542 is, for example, made of lead zirconate (PbZrO3) or lead titanate (PbTiO3). It should be noted that the main constituent material refers to the material containing more than 50% of the constituent material of the layer.

[0137] By using a multi-layered first hydrogen absorption layer 54A, hydrogen can be more effectively suppressed from entering the piezoelectric layer 53 compared to a single layer.

[0138] Furthermore, the hydrogen absorption performance, i.e., the amount of hydrogen absorbed, of the first absorber layer 541 and the second absorber layer 542 can be different from each other, or they can be the same. In addition, the second absorber layer 542 can also function as the aforementioned orientation control layer.

[0139] It should be noted that in the first embodiment and the first variation, a portion of the lower electrode 51 may be considered as part of the first hydrogen absorption layer 54. In this case, the first hydrogen absorption layer 54 is also considered to be composed of multiple layers. For example, the second electrode layer 512 of the lower electrode 51 may also be considered as part of the first hydrogen absorption layer 54. In addition, the first hydrogen absorption layer 54 may also function as an electrode.

[0140] 2-2. Second variation example

[0141] Figure 14This is a cross-sectional view of the piezoelectric element 5 in the second modified example. (See attached image.) Figure 14 As shown, a protective film 6 is disposed on the upper surface of the piezoelectric layer 53. Specifically, the protective film 6 is disposed on one end of the piezoelectric layer 53 along the X-axis. A portion of the upper surface of the piezoelectric layer 53 is exposed and not covered by the upper electrode 52. The protective film 6 is disposed on this exposed portion. The protective film 6 may contain, for example, ceramics such as alumina (AlOx) and silicon nitride.

[0142] By providing a protective film 6 on the exposed portion of the piezoelectric layer 53, hydrogen can be suppressed from entering the piezoelectric layer 53. Furthermore, a portion of the protective film 6 is sandwiched between the upper electrode 52. Specifically, a third electrode layer 521, a fourth electrode layer 522, and a fifth electrode layer 523 are disposed below the protective film 6. A third hydrogen absorption layer 524 is disposed above the protective film 6. By providing a portion of the third hydrogen absorption layer 524, hydrogen in the protective film 6 can be absorbed by the third hydrogen absorption layer 524, and hydrogen in the protective film 6 can be suppressed from entering the piezoelectric layer 53.

[0143] It should be noted that the third hydrogen absorption layer 524 can also be disposed below the protective film 6. In addition, although the third hydrogen absorption layer 524 is disposed on a portion of the upper surface of the protective film 6, it can also be disposed on the entire upper surface of the protective film 6.

[0144] Furthermore, when a protective film 6 is provided, in the manufacturing method of the piezoelectric element 5, after the formation of the third electrode layer 521, the fourth electrode layer 522, and the fifth electrode layer 523, the protective film 6 is formed during the formation of the third hydrogen absorption layer 524. The protective film 6 is mainly formed on the exposed portion of the upper surface of the piezoelectric layer 53 where the third electrode layer 521, the fourth electrode layer 522, and the fifth electrode layer 523 are not provided. The protective film 6 is formed by depositing a ceramic material using sputtering, vapor deposition, or CVD.

[0145] 2-3. Other variations

[0146] A "liquid ejector head" can also be a circulating head with a so-called circulating flow path.

[0147] Image forming apparatuses are used not only in printing but also in various other equipment such as fax machines and copiers. Their applications are not limited to printing. For example, an image forming apparatus that ejects a solution of color material can be used as a manufacturing apparatus for color filters in display devices such as liquid crystal display panels. Furthermore, an image forming apparatus that ejects a solution of conductive material can be used as a manufacturing apparatus for wiring and electrodes in wiring substrates. Additionally, an image forming apparatus that ejects a solution of organic matter related to living organisms can be used, for example, as a manufacturing apparatus for biochips.

[0148] The present invention has been described above based on preferred embodiments, but the present invention is not limited to the foregoing embodiments. Furthermore, the configurations of the various parts of the present invention can be replaced with any configuration that performs the same function as the foregoing embodiments, and any additional configurations can be added.

Claims

1. A piezoelectric element characterized by comprising: the piezoelectric element has a piezoelectric layer composed of a plurality of layers and a pair of electrodes disposed sandwiching the piezoelectric layer, the piezoelectric layer is composed of lead zirconate titanate, an average value of a hydrogen content ratio of the plurality of layers in the center of the piezoelectric layer is set as H(Ave), a maximum value is set as H(max), a minimum value is set as H(min), a larger one of an absolute value of (H(max)-H(ave)) / H(ave)) or (H(min)-H(ave)) / H(ave)) is set as ΔH as a variation rate of the hydrogen content ratio, and ΔH is 24% or less.

2. The piezoelectric element according to claim 1, characterized in that: the variation rate ΔH is 20% or less.

3. The piezoelectric element according to claim 1, characterized in that: in the plurality of layers in the center of the piezoelectric layer, an average hydrogen content ratio of a layer below in a stacking direction is smaller than an average hydrogen content ratio of a layer above.

4. The piezoelectric element according to claim 1, characterized in that: in one of the plurality of layers in the center of the piezoelectric layer, a hydrogen content ratio on a lower side is larger than a hydrogen content ratio on an upper side.

5. The piezoelectric element according to any one of claims 1 to 4, characterized in that: a film thickness of one of the plurality of layers in the center is 100 nm or more and 300 nm or less.

6. The piezoelectric element according to any one of claims 1 to 4, characterized in that: an average value of a titanium content ratio of the plurality of layers is set as Ti(Ave), a maximum value is set as Ti(max), a minimum value is set as Ti(min), a larger one of an absolute value of (Ti(max)-Ti(ave)) / Ti(ave)) or (Ti(min)-Ti(ave)) / Ti(ave)) is set as ΔTi as a variation rate of the titanium content ratio, and ΔTi is 14% or less.

7. The piezoelectric element according to any one of claims 1 to 4, characterized in that: the piezoelectric element has a hydrogen absorbing layer at a position sandwiching the piezoelectric layer in a stacking direction of the plurality of layers.

8. A liquid ejection head characterized by comprising: the liquid ejection head has the piezoelectric element according to claim 1.

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