Piezoelectric element and liquid ejection head

Abstract

The invention relates to a piezoelectric element and a liquid ejection head. Provided are a piezoelectric element having excellent displacement characteristics and a liquid ejection head including such a piezoelectric element. The piezoelectric element has a piezoelectric layer composed of a plurality of layers and a pair of electrodes disposed so as to sandwich the piezoelectric layer, the piezoelectric layer is composed of lead zirconate titanate, and the average value, the maximum value, and the minimum value of the hydrogen content contained in one layer in the center of the plurality of layers are H (Ave), H (max), and H (min) respectively, where H (Ave) is the average value of the hydrogen content, H (max) is the maximum value of the hydrogen content, and H (min) is the minimum value of the hydrogen content contained in one layer in the center of the plurality of layers. 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 DeltaH as the rate of change in the content of hydrogen, DeltaH is 21% or less.

Description

Technical Field

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

[0002] Previously, image forming apparatuses have been proposed that have liquid ejection heads that eject liquids such as ink from media such as printing paper. As such liquid ejection heads, the following heads are known: liquids filled in the pressure chamber are ejected from a nozzle by vibrating a vibrating plate that forms the wall of the pressure chamber using a piezoelectric element.

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

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

[0005] Patent Document 1 describes a piezoelectric layer composed of multiple layers formed by a sol-gel method. Each of these multiple layers is formed by firing a precursor film after a coating solution containing an organic compound is formed, dried, and gelled. By repeatedly performing the film formation and firing of the precursor film, a piezoelectric layer composed of multiple layers is formed.

[0006] For this piezoelectric element, it is known that compositional gradients exist between layers based on the material's crystallization temperature. For example, in the case where the piezoelectric layer is lead zirconate titanate, due to the difference in crystallization temperatures between lead titanate and lead zirconate, titanium tends to segregate more at the boundaries where crystallization occurs more rapidly. Therefore, sometimes the composition differs between the vicinity of the boundaries and the center of the layers. Such compositional gradients can potentially affect the displacement characteristics of the piezoelectric element.

[0007] Furthermore, the inventors of this invention have discovered through in-depth research that the displacement characteristics of a piezoelectric element vary depending on the hydrogen content of the piezoelectric layer. This phenomenon occurs even in piezoelectric elements with the same compositional gradient. In particular, the inventors of this invention have found that the rate of change of the 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 between the piezoelectric layer, wherein the piezoelectric layer is composed of lead zirconate titanate, and when the average value of the hydrogen content contained in the central layer of the multiple layers 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 21% 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 structure 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 cross-sectional view of a portion 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 a schematic representation Figure 4 The diagram shows a piezoelectric element.

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

[0017] Figure 8 This is a graph showing the measurement results of the piezoelectric element of Example 1 using a secondary ion mass spectrometer (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 using a secondary ion mass spectrometer.

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

[0021] Figure 12 It means 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 layer; 332...Second vibrating 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...Central 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 various parts in the drawings may differ appropriately from actual dimensions, and some parts may be shown schematically for ease of understanding. Furthermore, the scope of the present invention is not limited to these embodiments unless specifically defined in the following description. Additionally, "element β on element γ" is not limited to structures where element γ and element β are in direct contact, but also includes structures where element γ and element β are not in direct contact. "Element γ and element β are the same" means that element γ and element β are substantially the same, including manufacturing errors, etc. Furthermore, "element α and element β are stacked" means that element α and element β are arranged vertically, regardless of whether element α and element β are 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 structure 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 will be referred to as the X1 direction, and the direction opposite to the X1 direction will be referred to as the X2 direction. Similarly, one direction along the Y-axis will be referred to as the Y1 direction, and the direction opposite to the Y1 direction will be referred to as the Y2 direction. One direction along the Z-axis will be referred to as the Z1 direction, and the direction opposite to the Z1 direction will be referred to as the Z2 direction. Viewing along the Z-axis is referred to as "top view." Furthermore, the "stack direction" is the direction along the Z-axis. Typically, the Z-axis is 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, typically, the X-axis, Y-axis, and Z-axis are orthogonal to each other, but this is not a limitation; 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. Typically, the medium 90 is printing paper, but any material such as resin film or fabric can be used as the printing medium 90. Figure 1 As illustrated, the image forming apparatus 100 is provided with a liquid container 9 for storing ink. For example, a detachable box, a bag-shaped 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 uniformly controls all elements of the image forming apparatus 100.

[0032] The media conveying mechanism 22 conveys the medium 90 along the Y-axis under the control of the control unit 20. Furthermore, the moving mechanism 24, 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. Alternatively, a structure in which multiple liquid nozzles 3 are mounted on the conveyor body 242 or a structure in which the liquid container 9 is mounted together with the liquid nozzles 3 on the conveyor body 242 may also be used.

[0033] Under the control of the control unit 20, the liquid ejector head 3 ejects ink supplied from the liquid container 90 from multiple nozzles onto the medium 90. By ejecting ink onto the medium 90 from each liquid ejector head 3 in parallel with the repeated reciprocating motion of the medium 90 conveyed by the medium conveying mechanism 22 and the conveyor body 242, an image is formed on the surface of the medium 90.

[0034] Alternatively, the image forming apparatus 100 is a serial head type in which the liquid ejector head 3 reciprocates on the medium 90. However, the image forming apparatus 100 may also be a line 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 cross-sectional view of a portion 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. Furthermore, 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, spaced apart from each other along the X-axis. Each of the first column La and the second column Lb is a collection of a plurality of nozzles N arranged linearly along the Y-axis. The liquid nozzle 3 is configured in a substantially symmetrical manner, with 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 arranged as if facing each other. In the following description, the elements corresponding to the first column La are described in detail, while the description of the elements corresponding to the second column Lb is appropriately omitted.

[0038] like Figure 2 as well as Figure 3 As illustrated, the liquid ejector head 3 includes: a flow channel 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 frame portion 36, and a wiring substrate 40. The flow channel forming substrate 31, pressure chamber substrate 32, vibrating plate 33, nozzle plate 37, vibration absorber 38, sealing body 35, and frame portion 36 are each a long, plate-like member along the Y-axis. Furthermore, the nozzle plate 37, flow channel forming substrate 31, pressure chamber substrate 32, vibrating plate 33, and sealing body 35 are arranged sequentially along the Z2 direction.

[0039] Nozzle plate 37 is a plate-shaped member 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, for example, bonded to the Z1 direction surface of flow channel forming substrate 31 by an adhesive.

[0040] The flow channel forming substrate 31 forms a flow channel for ink flow. Specifically, the flow channel forming substrate 31 has a space Ra, a relay liquid chamber Rb, a plurality of supply channels 312, and a plurality of connecting channels 314. The space Ra is an elongated opening formed along the Y-axis. The supply channels 312 and the connecting channels 314 are each through holes formed for each nozzle N. When viewed from the Z1 direction, each connecting channel 314 overlaps with a corresponding nozzle N. The relay liquid chamber Rb is an elongated space formed along the Y-axis throughout the plurality of nozzles N, and the space Ra is interconnected with the plurality of supply channels 312. A pressure chamber substrate 32 is bonded to the Z2 direction surface of the flow channel forming substrate 31 by 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 by the inner wall surface 32a of the pressure chamber substrate 32. Pressure chambers C1 are formed for each nozzle N. Each pressure chamber C1 is an elongated space extending along the X1 direction. Multiple pressure chambers C1 are arranged along the Y-axis. Each pressure chamber C1 communicates with the connecting flow channel 314 and the supply flow channel 312. Therefore, the pressure chamber C1 communicates with the nozzle N via the connecting flow channel 314 and with the space Ra via the supply flow channel 312 and the relay liquid chamber Rb.

[0042] The nozzle plate 37, the flow channel 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. However, the nozzle plate 37, the flow channel forming substrate 31, and the pressure chamber substrate 32 can be manufactured using any known materials and methods.

[0043] The vibrating plate 33 is connected to the surface of the pressure chamber substrate 32 opposite to the flow channel 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 member that is elongated along the Y-axis when viewed from above. Alternatively, the vibrating plate 33 and the pressure chamber can be an integral structure, or they can be separately constructed and bonded together 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 arranged in each pressure chamber C1. The piezoelectric element 5 is elongated along the X-axis when viewed from above. The piezoelectric element 5 is a drive element that is driven by an applied drive 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 plurality of piezoelectric elements 5 and strengthens the mechanical strength of the pressure chamber substrate 32 and the vibrating plate 33. A recess is formed in the sealing body 35 on the surface opposite to the vibrating plate 33. The plurality of piezoelectric elements 5 are housed inside the recess. In addition, the sealing body 35 has a space 353 for the wiring substrate 40 to be inserted.

[0046] The frame portion 36 is bonded to the flow channel forming substrate 31, for example, by an adhesive. The frame portion 36 is a housing for storing ink supplied to the plurality of pressure chambers C1. The frame 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 frame portion 36. The supply port 361 is a conduit from the liquid container 9 that supplies ink and communicates with the space Rc. The space Rc communicates with the space Ra of the flow channel 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 the plurality of 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 the plurality of pressure chambers C1 in parallel from the relay liquid chamber Rb to each supply flow channel 312. Furthermore, when viewed from above, the space 362 overlaps with the space 353 of the sealing body 35. Wiring substrate 40 is inserted into spaces 353 and 362.

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

[0048] Furthermore, the vibration absorber 38 is bonded, for example, to the Z1 direction surface of the flow channel forming substrate 31 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 such a liquid ejector head 3, if the piezoelectric element 5 flexes and deforms due to the application of voltage, the vibrating plate 33 flexes and deforms in the direction that the volume of the pressure chamber C1 decreases, i.e., vibrates. 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. In addition, after the ink is ejected, the piezoelectric element 5 returns to its original position.

[0050] In addition, the liquid ejector head 3 has all Figure 3The structural elements shown are not all of these elements, but the liquid nozzle 3 may also have additional elements.

[0051] 1-3. Piezoelectric element 5

[0052] Figure 4 as well as Figure 5 Each represents 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 along the Z-axis, which is the stacking direction. Furthermore, although 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. Additionally, 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, although 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 each correspond to a "hydrogen absorption layer".

[0054] like Figure 4 as well as Figure 5 As shown, the lower electrode 51 is disposed above the vibrating plate 33. The lower electrode 51 is a separate electrode disposed for each piezoelectric element 5. A driving signal that varies the 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 from each other 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 across multiple piezoelectric elements 5. The piezoelectric layer 53 is, for example, a strip extending along the Y-axis and separated for each piezoelectric element 5 by forming multiple slits. 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 a plurality of 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. By applying a voltage between the lower electrode 51 and the upper electrode 52, the piezoelectric layer 53 is deformed, thereby causing the piezoelectric element 5 to flex and vibrate.

[0058] The vibrating plate 33 vibrates under the drive of 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 made of silicon oxide (SiO2). x The second vibrating body layer 332 is formed of elastic materials such as zirconium oxide (ZrO2). x 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. Furthermore, the vibrating plate 33 may consist of one layer or three or more layers.

[0059] Figure 4 The figure shows the neutral axis A1 of the vibrating plate 33. The neutral axis A1 is the position where the compressive force and the contraction 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. Each conductor 381 and 382 is a strip-shaped conductive film disposed along the edge of the upper electrode 52 in the X1 or X2 direction and extending in the direction along the Y-axis. Conductors 381 and 382 are made of, for example, a conductive material with low resistance such as gold. Conductors 381 and 382 suppress voltage drop of the reference voltage of the upper electrode 52. Furthermore, conductors 381 and 382 also function as weights that define the vibration area of ​​the vibrating plate 33. Alternatively, conductors 381 and 382 may be omitted.

[0061] Furthermore, 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. In addition, the upper electrode 52 is electrically connected to the aforementioned wiring substrate 40 via wiring (not shown).

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

[0063] Figure 6It is a schematic representation Figure 4 The diagram shows the piezoelectric element 5. As described above, the piezoelectric element 5 has 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. Furthermore, 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 layers constituting the piezoelectric body layer 53. In addition, the upper electrode 52 has a third hydrogen absorption layer 524. The first hydrogen absorption layer 54 and the third hydrogen absorption layer 524 each correspond to a "hydrogen absorption layer".

[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. Furthermore, 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 or equal to the thickness of the first electrode layer 511.

[0066] In this embodiment, the lower electrode 51 is composed of two layers, but it can also be composed of one layer or three or more layers. Furthermore, the first electrode layer 511 and the second electrode layer 512 can be made of 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 piezoelectric layer 53 in the stacking direction of the piezoelectric element 5, i.e., along the Z-axis. The first hydrogen absorption layer 54 has the function of absorbing hydrogen. According to the piezoelectric element 5 having such a first hydrogen absorption layer 54, hydrogen present at the boundary between the lower electrode 51 and other layers, hydrogen present in the piezoelectric layer 53, or hydrogen that may enter the piezoelectric layer 53 can be absorbed.

[0068] in addition, Figure 6In this design, the boundary between the first hydrogen absorption layer 54 and the piezoelectric layer 53 is clearly defined, but it may not be. For example, a portion of the first hydrogen absorption layer 54 may be embedded in the piezoelectric layer 53, dispersed in the piezoelectric layer 53, or integrated with the piezoelectric layer 53. Furthermore, the composition within the first hydrogen absorption layer 54 may be constant or gradient. Therefore, the composition may differ between the piezoelectric layer 53 side and the lower electrode 51 side of the first hydrogen absorption layer 54. Furthermore, 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. Additionally, the first hydrogen absorption layer 54 may be composed of 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 number of layers in the piezoelectric layer 53 is not limited to 6; it can be 5 or fewer, or 7 or more. However, the piezoelectric layer 53 is composed of multiple layers rather than a single layer, thereby enabling the formation of a piezoelectric layer 53 with excellent piezoelectric properties.

[0070] Each layer constituting the piezoelectric layer 53 is composed of a perovskite-type composite oxide. More specifically, each layer is composed of lead zirconate titanate (PZT: Pb(Zr,Ti)O3). In addition, the piezoelectric layer 53 may also contain at least one element selected from vanadium (V), niobium (Nb), tantalum (Ta), nickel (Ni), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi).

[0071] Furthermore, the thickness of each layer of the piezoelectric layer 53 is not particularly limited, but for example, it is above 90 nm and below 250 nm.

[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 appropriately absorbs hydrogen in the first layer 531 and the second layer 532.

[0074] in addition, Figure 6In this embodiment, the boundary between the second hydrogen absorption layer 55 and the second layer 532, and the boundary between the second hydrogen absorption layer 55 and the first layer 531, are each clearly defined, but 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, dispersed in the first layer 531 or the second layer 532, or integrated with the first layer 531 or the second layer 532. Furthermore, the composition within the second hydrogen absorption layer 55 may be constant or gradient. Therefore, the composition may differ between the second layer 532 side and the first layer 531 side of the second hydrogen absorption layer 55. Furthermore, 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. In this embodiment, the film thickness of the second hydrogen absorption layer 55 is thinner than the film thickness of the first hydrogen absorption layer 54, but may also be greater than or equal to the film thickness 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 sequentially stacked. 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, for example, contains iridium oxide (IrO). x 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, for example, contains titanium oxide (TiO2). x 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 such a third hydrogen absorption layer 524, compared to not providing it, 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 appropriately absorbs hydrogen from the upper electrode 52. Furthermore, the composition within the third hydrogen absorption layer 524 can be constant or gradient. Moreover, it can be formed from multiple layers.

[0078] in addition, 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 a configuration control layer can be provided. Furthermore, the first hydrogen absorption layer 54 can also function as such an orientation control layer. Since the first hydrogen absorption layer 54 functions as an orientation control layer, there is no need to provide a separate orientation control layer, thus simplifying manufacturing. Additionally, the orientation control layer can, for example, preferentially orient the crystals above it in a predetermined planar orientation, or adjust the degree of orientation of the predetermined planar orientation.

[0079] Similarly, while 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 can be provided. The second hydrogen absorption layer 55 can also function as such an orientation control layer. Since the second hydrogen absorption layer 55 functions as such an orientation control layer, there is no need to provide a separate orientation control layer, thus simplifying manufacturing.

[0080] 1-4. Piezoelectric layer

[0081] As described above, the piezoelectric layer 53 is composed of multiple layers. The piezoelectric layer 53 is configured with a lower electrode 51 and an upper electrode 52 sandwiched between them, which serve as a pair of electrodes. The multiple layers constituting the piezoelectric layer 53 have a "central layer." In this embodiment, the "central layer" is either the third layer 533 or the fourth layer 534. The "central layer" is a layer located at or near the center of the piezoelectric layer 53, and is not in contact with the upper electrode 52 and the lower electrode 51 located above or below the piezoelectric layer 53; it is a layer sandwiched between the other layers of the piezoelectric layer 53. Furthermore, when the piezoelectric layer is composed of three or more layers, the layer located at or near the center of the piezoelectric layer 53 corresponds to the "central layer."

[0082] The following explanation will focus on the case of the third layer 533, specifically the "central layer 1". The rate of change of hydrogen content ΔH in the third layer 533 is less than 21%.

[0083] The rate of change ΔH is the greater 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 analysis.

[0085] The rate of change of hydrogen content ΔH in the third layer 533, which is the "central layer 1", is less than 21%, thus suppressing the reduction of displacement characteristics of the piezoelectric element compared to cases where ΔH exceeds 21%.

[0086] The hysteresis characteristics of the piezoelectric element 5 vary over time depending on the hydrogen content of the piezoelectric layer 53, resulting in a significant change from the design stage. As a result, the displacement characteristics of the piezoelectric element 5 decrease over time. Furthermore, this leads to a change in the amount of displacement obtained based on the driving voltage value set during the design stage. This decrease in displacement characteristics is more significant when the piezoelectric layer 53 is formed from multiple layers. Although described later, the piezoelectric layer 53 is formed by repeatedly forming and firing multiple layers. It is believed that hydrogen enters into the piezoelectric layer 53 during this manufacturing process, thereby changing the hydrogen content of the piezoelectric layer 53. Moreover, when comparing multiple piezoelectric elements 5, even when the same compositional gradient is generated in the piezoelectric layer 53, it was found that the displacement characteristics of the piezoelectric element 5 decrease depending on the hydrogen content.

[0087] As a result of in-depth research, the inventors discovered that by suppressing the rate of change ΔH of the hydrogen content in the central third layer 533 of the piezoelectric layer 53, the decrease in the displacement characteristics of the piezoelectric element 5 over time can be suppressed. Specifically, this rate of change ΔH is 21% or less, thereby suppressing the decrease in the displacement characteristics of the piezoelectric element 5. Furthermore, by suppressing the decrease in the displacement characteristics of the piezoelectric element 5 relative to the design stage, it is not necessary to adjust the driving voltage or waveform to match the change over time, thus improving ease of use.

[0088] The central layer of 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 piezoelectric layer 53 that is separated from the central axis A1, the higher the performance of the piezoelectric element 5. It is believed that by suppressing the rate of change ΔH of the hydrogen content in the central layer to a smaller extent, the rate of change of the hydrogen content in other layers is reduced, further reducing the average hydrogen content in the piezoelectric layer 53.

[0089] Furthermore, the central layer is not in contact with the upper electrode 52 or the lower electrode 51, and is sandwiched between other layers of the piezoelectric layer 53. Therefore, the influence from the upper electrode 52 and the lower electrode 51 can be suppressed to determine the hydrogen content. For example, when measuring the layer in contact with the upper electrode 52 or the lower electrode 51 by secondary ion mass analysis, the measurement is sometimes 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 sometimes changes significantly due to the boundary effect. If the central layer, which is not in contact with the upper electrode 52 or 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] The rate of change ΔH of hydrogen content in the third layer 533 is less than 21%, thereby suppressing the increase in the difference in displacement between the multiple piezoelectric elements 5. Therefore, it eliminates the need to change the driving voltage and waveform for each piezoelectric element 5 to adjust for the difference in displacement between the multiple piezoelectric elements 5. This improves the ease of use of the piezoelectric elements 5.

[0091] Furthermore, in this embodiment, the rate of change ΔH in the fourth layer 534 is also 21% or less, just like the rate of change ΔH in the third layer 533. Specifically, as long as either the rate of change ΔH in the fourth layer 534 or the rate of change ΔH in the third layer 534 is 21% or less, the reduction in the displacement characteristics of the piezoelectric element 5 can be suppressed compared to cases where it exceeds 21%.

[0092] Furthermore, the rate of change ΔH of the hydrogen content in the aforementioned third layer 533 can be 21% or less, but more preferably 16% or less. By making the rate of change ΔH 16% or less, the reduction in the displacement characteristics of the piezoelectric element 5 can be more suppressed compared to the case where it exceeds 16%.

[0093] Preferably, the rate of change ΔH in the fourth layer 534 is also 16% or less, just like the rate of change ΔH in the third layer 533. However, as long as either the rate of change ΔH in the fourth layer 534 or the rate of change ΔH in the third layer 534 is 16% or less, the reduction in the displacement characteristics of the piezoelectric element 5 can be suppressed compared to the case where it exceeds 16%.

[0094] Furthermore, it is preferable that the hydrogen content on the lower side of the third layer 533 is greater than the hydrogen content on the upper side of the third layer 533. In other words, in the third layer 533, the hydrogen content at the position of the piezoelectric layer 53 away from the neutral axis A1 is lower. Therefore, it is possible to suppress the reduction of the displacement characteristics of the piezoelectric element 5.

[0095] Similarly, it is preferable that the hydrogen content on the lower side of the fourth layer 534 is greater than the hydrogen content on the upper side of the fourth layer 534. Alternatively, in the third layer 533 and the fourth layer 544, the hydrogen content on the lower side may be less than the hydrogen content on the upper side. Furthermore, the lower side of a 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 a 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 in this range is determined, for example, using secondary ion mass analysis.

[0096] Furthermore, the thickness D3 of the third layer 533, which is the central layer among the multiple layers constituting the piezoelectric layer 53, is not particularly limited, but is preferably 100 nm or more and 300 nm or less.

[0097] Although described later, the manufacturing process of the piezoelectric layer 53 sometimes includes a degreasing process and a firing process. In this case, there is a risk that hydrogen in the precursors constituting each layer of the piezoelectric layer 53 may not be completely removed during the degreasing process, or that hydrogen may enter the piezoelectric layer 53 during the firing process. In particular, when the piezoelectric layer 53 is formed using the sol-gel method, the possibility of incomplete hydrogen removal is high. By making the film thickness D3 100 nm or more and 300 nm or less, hydrogen is more easily removed during the degreasing process compared to cases outside this range, and the firing process time is shortened, thereby making it less likely for hydrogen to enter.

[0098] Similarly, the thickness D4 of the fourth layer 534, which is the central layer among the multiple layers constituting the piezoelectric layer 53, is not particularly limited, but is preferably 100 nm or more and 300 nm or less.

[0099] 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 third layer 533 is preferably 13% or less.

[0100] 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)).

[0101] Ti(Ave) is the average content of titanium in the third layer 533. Ti(max) is the maximum content of titanium in the third layer 533. Ti(min) is the minimum content of titanium in the third layer 533. Ti(Ave), Ti(max), and Ti(min) are determined, for example, by secondary ion mass analysis.

[0102] The compositional gradient of titanium in the piezoelectric layer 53 affects the displacement characteristics of the piezoelectric element 5. The rate of change ΔTi in the central third layer 53 of the piezoelectric layer 53 is less than 13%, thus suppressing the titanium compositional gradient in the piezoelectric layer 53 compared to cases exceeding 13%. Therefore, the displacement characteristics of the piezoelectric element 5 can be improved. Furthermore, titanium has high hydrogen storage capacity. Therefore, when the deviation in titanium content is large, the deviation in hydrogen content in the piezoelectric layer 53 becomes larger. Therefore, by suppressing the deviation in titanium content, the deviation in hydrogen content can be suppressed. As a result, the reduction in the displacement characteristics of the piezoelectric element 5 can be suppressed.

[0103] Preferably, the rate of change ΔTi in the fourth layer 534 is also 13% or less, just like the rate of change ΔTi in the third layer 533. However, as long as either the rate of change ΔTi in the fourth layer 534 or the rate of change ΔTi in the third layer 534 is 13% or less, the reduction in the displacement characteristics of the piezoelectric element 5 can be suppressed compared to the case where it exceeds 13%.

[0104] Furthermore, 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 at positions sandwiching the piezoelectric layer 53 in the stacking direction of the multiple layers constituting the piezoelectric layer 53. The piezoelectric layer 53 is disposed between the first hydrogen absorption layer 54 and the third hydrogen absorption layer 524.

[0105] Hydrogen in the piezoelectric layer 53 is generated during the degreasing and firing of the precursor, and also increases due to 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.

[0106] 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.

[0107] Furthermore, the first hydrogen absorption layer 54 is made of a material capable of absorbing hydrogen. Specifically, the first hydrogen absorption layer 54 contains a hydrogen storage material that can combine with hydrogen to form a hydride. The hydrogen storage material absorbs or releases hydrogen depending on 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).

[0108] 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.

[0109] Furthermore, the piezoelectric layer 53 is composed of lead zirconate titanate (PZT), a perovskite-type composite oxide, as described above. Since the piezoelectric layer 53 is PZT, it particularly effectively suppresses changes in the hysteresis characteristics of the piezoelectric element 5 by providing the first hydrogen absorption layer 54.

[0110] 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 comprise titanium. It is even more preferred that these layers are each composed of titanium. Titanium has excellent hydrogen absorption properties. Therefore, because these layers comprise titanium, they can absorb more hydrogen that could potentially enter the piezoelectric layer 53 compared to the case where they do not.

[0111] Figure 7 This is a table showing the embodiments and comparative examples. Figure 7 Examples 1-10 and Comparative Examples 1-6 are shown. Examples 1-10 and Comparative Examples 1-6 each have six piezoelectric layers 53. The film thickness of each piezoelectric layer 53 is approximately 220 nm. Furthermore, Figure 7 The results and evaluations of the hydrogen content, change rate ΔTi, and ΔH in the third layer 533, determined and calculated by secondary ion mass analysis, are shown. However, similar results and evaluation trends were obtained in the fourth layer 534.

[0112] 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 third layer 533 differ for Examples 1-10 and Comparative Examples 1-6. The hydrogen concentration in the third layer 533 is adjusted by varying the heating conditions and the amount of hydrogen in the hydrogen absorption layer during the manufacturing process. Besides… Figure 7 The illustrated embodiments Figure 6 In addition to the structure of the piezoelectric element 5 shown, examples of structures with structures 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.

[0113] like Figure 7As shown, in Examples 1-10, for the rate of change ΔH of hydrogen content in the third layer 533, the larger of the absolute values ​​of (H(max)-H(ave)) / H(ave)) or (H(min)-H(ave)) / H(ave)) is 21% or less. On the other hand, in Comparative Examples 1-6, for the rate of change ΔH of hydrogen content in the third layer 533, the larger of the absolute values ​​of (H(max)-H(ave)) / H(ave)) or (H(min)-H(ave)) / H(ave)) exceeds 21%.

[0114] Each embodiment exhibits superior displacement characteristics compared to the comparative examples. The evaluation is based on the rate of displacement change of the piezoelectric element 5 over time. A durability test was conducted on a liquid nozzle equipped with the piezoelectric element 5, applying predetermined driving pulses continuously for 10 billion cycles. The rate of displacement reduction of the piezoelectric element 5 over time before and after the application of the predetermined driving pulses was determined. The predetermined driving pulse is 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%.

[0115] As described above, the rate of change ΔH in Examples 1-10 is less than 21%, while the rate of change ΔH in Comparative Examples 1-6 exceeds 21%. Therefore, the rate of displacement change of the piezoelectric element 5 over time is lower in each embodiment than in the comparative examples. Thus, Examples 1-10 are able to suppress the displacement change of the piezoelectric element 5 over time compared to Comparative Examples 1-6. As a result, Examples 1-10 are able to suppress the reduction in the displacement characteristics of the piezoelectric element. Therefore, the liquid ejector head 3 equipped with the piezoelectric element 5 of Examples 1-10 can exhibit excellent ejection characteristics.

[0116] Furthermore, in Examples 1, 2, 5, 7-10, the rate of change ΔH of the hydrogen content in the third layer 533 is less than 16%. For Examples 1, 2, 5, 7-10, the rate of change over time is less than -3.0%, which is very small. Therefore, Examples 1, 2, 5, 7-10 can improve the displacement characteristics of the piezoelectric element 5 compared to other examples. Therefore, the liquid ejector head equipped with the piezoelectric element 5 of Examples 1, 2, 5, 7-10 can exhibit particularly excellent ejection characteristics.

[0117] Furthermore, in Examples 1-10, the rate of change ΔTi of titanium content in the third layer 533 was less than 13%. Figure 7 Although not illustrated, the thickness D3 of the third layer 533 is approximately 220 nm. Furthermore, the piezoelectric element 5 of Examples 1-10 has a first hydrogen absorption layer 54 and a third hydrogen absorption layer 524.

[0118] 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 in 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.

[0119] Furthermore, 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 comprises titanium. The second hydrogen absorption layer 55 comprises 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. In addition, Examples 2 and Comparative Examples 1 and 2 have the protective film 6 shown in the third modified example described later.

[0120] Figures 8-11 The horizontal axis represents the depth [nm]. Analysis was performed on the upper electrode 52 along the Z1 direction; therefore, the shallower depth is on the upper electrode 52 side, and the deeper depth is on the lower electrode 51 side. Figures 8-11 The vertical axis represents the hydrogen concentration [atoms / cc]. This hydrogen concentration is quantified using standard samples doped with the target element at known concentrations. For titanium and zirconium, it is expressed as ionic strength. Additionally, "E" indicates a power of 10. For example, 1E+20 represents 1 × 10⁻⁶. 20 1E+19 represents 1×10 19 .

[0121] In addition, Figures 8-11 In this process, distinct line segments are drawn along the boundaries of each layer, but the positions of the boundaries may deviate slightly depending on the interpretation. 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, for example, the hydrogen peaks occurring near the depths of the first and second hydrogen absorption layers 54 and 55 may be considered as peaks within the first and second hydrogen absorption layers 54 and 55, respectively.

[0122] Figures 8-11 Show H(max), H(min), Ti(max), and Ti(min). For Figure 8 The first embodiment and Figure 9 Each of the second embodiments, respectively, is related to Figure 10 The first comparative example and Figure 11Compared to the second comparative example, the rate of change ΔH of hydrogen content in the third layer 533 is smaller. Furthermore, for... Figure 8 The first embodiment and Figure 9 Each of the second embodiments, respectively, is related to 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 third layer 533 is smaller. Additionally, Figures 8-11 In this context, Ti is represented by its second ionic strength.

[0123] In addition, the H (Ave) and Ti (Ave) of the layer are calculated by averaging the hydrogen content and titanium content from one end boundary of the layer to the other end boundary.

[0124] In addition, Figure 8 The first embodiment and Figure 9 In each of the second embodiments, the hydrogen content on the lower side of the third layer 533 is greater than the hydrogen content on the upper side of the third layer 533. Furthermore, the lower side is deeper, and the upper side is shallower.

[0125] 1-5. Manufacturing method of piezoelectric element 5

[0126] Figure 12 It means 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.

[0127] 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 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 second electrode layer 512.

[0128] 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 on the layer containing the hydrogen storage material using a sol-gel method, and then degreased. Next, 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.

[0129] Next, other layers containing hydrogen storage materials such as titanium are formed on the first layer 531 using sputtering, vapor deposition, or CVD. Then, a second layer precursor composed of perovskite-type composite oxides such as PZT is formed on the other layers containing the hydrogen storage material using a sol-gel method, followed by degreasing. 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.

[0130] When forming the second hydrogen absorber layer 55, it is possible that the second hydrogen absorber layer 55 may be formed while 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 during its formation is reduced, allowing for sufficient hydrogen absorption by the formed second hydrogen absorber layer 55.

[0131] Next, after forming a third-layer precursor composed of perovskite-type composite oxides such as PZT on the second layer 532 using the sol-gel method, the third-layer precursor is fired. This forms the third layer 533. The fourth layer 534, fifth layer 535, and sixth layer 536 are formed using the same method. Then, after the sixth layer 536 is formed, the first hydrogen absorber layer 54, the second hydrogen absorber layer 55, and the piezoelectric layer 53 are fired together.

[0132] When each layer of the piezoelectric layer 53 is formed by the sol-gel method, the shape and crystallinity of the lower layer 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 the middle layer of the piezoelectric layer 53, i.e., the third layer 533, by sol-gel.

[0133] 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 forming a layer containing a conductive material such as iridium on a sixth layer 536 using sputtering, vapor deposition, or CVD, a firing process is performed to form a third electrode layer 521 containing a metal oxide or the like. Next, after forming a layer containing a conductive material such as titanium on the third electrode layer 521 using sputtering, vapor deposition, or CVD, a firing process is performed to form a fourth electrode layer 522 containing a metal oxide or the like.

[0134] 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, vapor deposition, or CVD. Then, 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, vapor deposition, or CVD. Based on the above, a piezoelectric element 5 is manufactured.

[0135] 2. Variations

[0136] The embodiments illustrated above can be modified in various ways. The following examples illustrate specific modifications that can be applied to the aforementioned embodiments. Two or more methods selected from the following examples can be appropriately combined without contradicting each other.

[0137] 2-1. First variation example

[0138] 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). In addition, the main constituent material refers to the material containing more than 50% of the materials constituting the layers.

[0139] The first hydrogen absorption layer 54A is composed of multiple layers, which can more effectively suppress the entry of hydrogen into the piezoelectric layer 53 compared to a single layer.

[0140] 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 the same. Additionally, the second absorber layer 542 can also function as the aforementioned orientation control layer.

[0141] Alternatively, 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. Furthermore, the first hydrogen absorption layer 54 may also function as an electrode.

[0142] 2-2. Second variation

[0143] Figure 14 This 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 includes, for example, ceramics such as alumina (AlOx) and silicon nitride.

[0144] A protective film 6 is disposed on the exposed portion of the piezoelectric layer 53, thereby suppressing hydrogen from entering the piezoelectric layer 53. Furthermore, a portion of the protective film 6 is held in place by 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, thereby suppressing hydrogen from the protective film 6 from entering the piezoelectric layer 53.

[0145] Alternatively, the third hydrogen absorption layer 524 can also be disposed below the protective film 6. Furthermore, the third hydrogen absorption layer 524 can be disposed on a portion of the upper surface of the protective film 6, but it can also be disposed over the entire upper surface of the protective film 6.

[0146] Furthermore, when a protective film 6 is provided, in the manufacturing method of the piezoelectric element 5, the protective film 6 is formed during the formation of the third hydrogen absorption layer 524 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 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 formed. The protective film 6 is formed by depositing ceramic material using sputtering, vapor deposition, or CVD.

[0147] 2-3. Other variations

[0148] A "liquid ejector head" can also be a circulating head with a so-called circulating flow channel.

[0149] Image forming apparatuses can be used not only in printing equipment but also in various other devices 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 in the manufacture of color filters for display devices such as liquid crystal display panels. Furthermore, an image forming apparatus that ejects a solution of conductive material can be used in the manufacture of wiring and electrodes for wiring substrates. Additionally, an image forming apparatus that ejects a solution of organic matter related to living organisms can be used, for example, in the manufacture of biochips.

[0150] The present invention has been described above based on preferred embodiments, but the present invention is not limited to the foregoing embodiments. Furthermore, the structure of each part of the present invention can be replaced with any structure that performs the same function as the foregoing embodiments, and any additional structure 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 arranged to sandwich the piezoelectric layer, The piezoelectric layer is composed of lead zirconate titanate, When an average value of a content ratio of hydrogen contained in the 1 layer at the center of the plurality of layers 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 content ratio of hydrogen, ΔH is 21% or less.

2. The piezoelectric element according to claim 1, wherein The variation rate ΔH is 16% or less.

3. The piezoelectric element according to claim 1, wherein In the 1 layer at the center of the plurality of layers, a hydrogen content rate on a lower side is greater than a hydrogen content rate on an upper side.

4. The piezoelectric element according to any one of claims 1 to 3, wherein A film thickness of the 1 layer at the center of the plurality of layers is 100 nm or more and 300 nm or less.

5. The piezoelectric element according to any one of claims 1 to 3, wherein When an average value of a content ratio of titanium contained in the 1 layer at the center 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 content ratio of titanium, ΔTi is 13% or less.

6. The piezoelectric element according to any one of claims 1 to 3, wherein The piezoelectric element has a hydrogen absorption layer at a position sandwiching the piezoelectric layer in a stacking direction of the plurality of layers.

7. A liquid ejection head, wherein The liquid ejection head has the piezoelectric element according to claim 1.

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