Piezoelectric element and liquid dispensing head

Abstract

To provide a piezoelectric element with excellent displacement characteristics, and a liquid dispensing head including such piezoelectric element. [Solution] The piezoelectric element comprises a piezoelectric layer consisting of multiple layers and a pair of electrodes arranged on either side of the piezoelectric layer, wherein the piezoelectric layer is composed of zirconate titanate, and when the average value H(Ave), maximum value H(max), and minimum value H(min) of the hydrogen content in the central layer of the multiple layers are defined as H(max), the maximum value as H(max), and the minimum value as H(min), and ΔH is the larger of the absolute values ​​of (H(max)-H(ave)) / H(ave)) or (H(min)-H(ave)) / H(ave)) as the rate of change of the hydrogen content, ΔH is 21% or less.

Description

Technical Field

[0001] The present invention relates to a piezoelectric element and a liquid ejection head.

Background Art

[0002] Conventionally, an image forming apparatus including a liquid ejection head that ejects a liquid such as ink onto a medium such as printing paper has been proposed. As the liquid ejection head, a head that ejects the liquid filled in a pressure chamber from a nozzle by vibrating a diaphragm that constitutes a wall surface of the pressure chamber with a piezoelectric element is known.

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

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The piezoelectric layer described in Patent Document 1 is composed of a plurality of layers formed by a sol-gel method. Each of the plurality of layers is formed by applying and drying a coating solution containing an organic compound to form a precursor film, and then firing the precursor film. A piezoelectric layer composed of a plurality of layers is formed by repeating the film formation and firing of the precursor film a plurality of times.

[0006] It is known that in piezoelectric elements, compositional gradients occur within each layer depending on the crystallization temperature of the material. For example, if the piezoelectric layer is made of lead zirconate titanate, the difference in crystallization temperatures between lead titanate and lead zirconate causes titanium to segregate more readily at the interface where crystallization proceeds more quickly. As a result, the composition may differ between the vicinity of the interface and the center of each layer. Such compositional gradients may affect the displacement characteristics of the piezoelectric element.

[0007] Furthermore, as a result of diligent research, the inventors have discovered that the displacement characteristics of a piezoelectric element change depending on the hydrogen content of the piezoelectric layer. This occurs even for piezoelectric elements with equivalent compositional gradients. In particular, the inventors have found that the rate of change in the hydrogen content in the central layer of the piezoelectric layer affects the displacement characteristics of the piezoelectric element. [Means for solving the problem]

[0008] A piezoelectric element according to a preferred embodiment of the present invention is a piezoelectric element having a piezoelectric layer consisting of a plurality of layers and a pair of electrodes arranged on either side of the piezoelectric layer, wherein the piezoelectric layer is composed of zirconate titanate, and when the average value H(Ave), maximum value H(max), and minimum value H(min) of the hydrogen content contained in the central layer of the plurality of layers are defined as H(Ave), the maximum value as H(max), and the minimum value as H(min), and ΔH is the larger of the absolute values ​​of (H(max)-H(ave)) / H(ave)) or (H(min)-H(ave)) / H(ave)) as the rate of change of the hydrogen content, ΔH is 21% or less.

[0009] A liquid dispensing head according to a preferred embodiment of the present invention has a piezoelectric element. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram illustrating the configuration of an image forming apparatus according to the first embodiment. [Figure 2] Figure 1 is an exploded perspective view of the liquid dispensing head. [Figure 3] This is a cross-sectional view of a portion of the liquid dispensing head shown in Figure 1. [Figure 4]Figure 3 is a cross-sectional view of the piezoelectric element shown. [Figure 5] Figure 3 is a cross-sectional view of the piezoelectric element shown. [Figure 6] This figure schematically illustrates the piezoelectric element shown in Figure 4. [Figure 7] This is a table showing examples and comparative examples. [Figure 8] This figure shows the measurement results of the piezoelectric element of Example 1 using a secondary ion mass spectrometer (SIMS). [Figure 9] This figure shows the measurement results of the piezoelectric element of Example 2 using a secondary ion mass spectrometer. [Figure 10] This figure shows the measurement results of the piezoelectric element of Comparative Example 1 using a secondary ion mass spectrometer. [Figure 11] This figure shows the measurement results of the piezoelectric element of Comparative Example 1 using a secondary ion mass spectrometer. [Figure 12] This diagram shows the manufacturing process for the piezoelectric element shown in Figure 6. [Figure 13] This diagram schematically shows the piezoelectric element of the first modified example. [Figure 14] This is a cross-sectional view of the piezoelectric element of the second modified example. [Modes for carrying out the invention]

[0011] Preferred embodiments of the present invention will be described below with reference to the attached drawings. Note that the dimensions or scale of each part in the drawings may differ from the actual dimensions as appropriate, and some parts are shown schematically for ease of understanding. Furthermore, the scope of the present invention is not limited to these embodiments unless otherwise stated in the following description. Also, "element β on element γ" is not limited to a configuration in which element γ and element β are in direct contact, but also includes configurations in which 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. Also, "element α and element β are stacked" means that element α and element β are aligned in the vertical direction, and it is not required that element α and element β are in direct contact.

[0012] 1. First Embodiment 1-1. Overall Configuration of Image Forming Apparatus 100 FIG. 1 is a schematic diagram illustrating the configuration of an image forming apparatus 100 according to the first embodiment. Hereinafter, for convenience of explanation, the X-axis, Y-axis, and Z-axis orthogonal to each other will be appropriately used for explanation. Also, one direction along the X-axis is denoted as the X1 direction, and the direction opposite to the X1 direction is denoted as the X2 direction. Similarly, one direction along the Y-axis is denoted as the Y1 direction, and the direction opposite to the Y1 direction is denoted as the Y2 direction. One direction along the Z-axis is denoted as the Z1 direction, and the direction opposite to the Z1 direction is denoted as the Z2 direction. Looking in the direction along the Z-axis is referred to as "plan view". Also, the "lamination direction" is the direction along the Z-axis. The Z-axis is typically a vertical axis. The Z2 direction is the upper side, and the Z1 direction is the lower side. However, the Z-axis does not necessarily have to be a vertical axis. Also, the X-axis, Y-axis, and Z-axis are typically orthogonal to each other, but are not limited thereto, and may intersect at an angle within a range of, for example, 80° or more and 100° or less.

[0013] The image forming apparatus 100 in FIG. 1 is an inkjet printing apparatus that discharges ink, which is an example of a liquid, onto a medium 90. The medium 90 is typically printing paper, but a printing target of any material such as a resin film or fabric can be used as the medium 90. As illustrated in FIG. 1, a liquid container 9 for storing ink is installed in the image forming apparatus 100. For example, a cartridge detachable from the image forming apparatus 100, a bag-shaped ink pack formed of a flexible film, or an ink tank capable of being refilled with ink is used as the liquid container 9.

[0014] The image forming apparatus 100 includes a control unit 20, a medium conveyance mechanism 22, a moving mechanism 24, and a liquid discharge head 3. The control unit 20 includes 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 comprehensively controls each element of the image forming apparatus 100.

[0015] The medium transport mechanism 22 transports the medium 90 in a direction along the Y-axis under the control of the control unit 20. The moving mechanism 24 reciprocates the liquid discharge head 3 along the X-axis under the control of the control unit 20. The moving mechanism 24 comprises a roughly box-shaped transport body 242 that houses the liquid discharge head 3 and a transport belt 244 to which the transport body 242 is fixed. A configuration in which multiple liquid discharge heads 3 are mounted on the transport body 242, or a configuration in which a liquid container 9 is mounted on the transport body 242 together with the liquid discharge head 3, may also be adopted.

[0016] The liquid ejection head 3 ejects ink supplied from the liquid container 9 onto the medium 90 from multiple nozzles under the control of the control unit 20. As the medium 90 is transported by the medium transport mechanism 22 and the transport body 242 moves back and forth repeatedly, each liquid ejection head 3 ejects ink onto the medium 90, forming an image on the surface of the medium 90.

[0017] The image forming apparatus 100 is a serial head system in which the liquid ejection head 3 moves back and forth on the medium 90. However, the image forming apparatus 100 may also be a line head system in which the liquid ejection head 3 is fixed.

[0018] 1-2. Overall configuration of liquid dispensing head 3 Figure 2 is an exploded perspective view of the liquid ejection head 3 shown in Figure 1. Figure 3 is a cross-sectional view of a part of the liquid ejection head shown in Figure 1, and is the cross-sectional view along line aa in Figure 2. The cross-section shown in Figure 3 is parallel to the XZ plane. The Z axis is the axis along the direction of ink ejection by the liquid ejection head 3.

[0019] As illustrated in Figure 2, the liquid discharge head 3 comprises a plurality of nozzles N arranged along the Y-axis. The plurality of nozzles N in the first embodiment are divided into a first row La and a second row Lb, which are spaced apart from each other and arranged side by side along the X-axis. Each of the first row La and the second row Lb is a collection of a plurality of nozzles N arranged linearly along the Y-axis. The liquid discharge head 3 has a structure in which the elements associated with each nozzle N in the first row La and the elements associated with each nozzle N in the second row Lb are arranged substantially symmetrically. In the following description, the elements corresponding to the first row La will be described in detail, and the descriptions of the elements corresponding to the second row Lb will be omitted as appropriate.

[0020] As illustrated in Figures 2 and 3, the liquid discharge head 3 comprises a flow path forming substrate 31, a pressure chamber substrate 32, a diaphragm 33, a nozzle plate 37, a vibration absorber 38, a plurality of piezoelectric elements 5, a sealant 35, a housing portion 36, and a wiring board 40. Each of the flow path forming substrate 31, pressure chamber substrate 32, diaphragm 33, nozzle plate 37, vibration absorber 38, sealant 35, and housing portion 36 is a long, plate-shaped member along the Y-axis. Furthermore, the nozzle plate 37, flow path forming substrate 31, pressure chamber substrate 32, diaphragm 33, and sealant 35 are arranged in this order in the Z2 direction.

[0021] The nozzle plate 37 is a plate-shaped member on which a plurality of nozzles N are formed. Each of the plurality of nozzles N is a circular through-hole for ejecting ink. The nozzle plate 37 is joined to the surface of the flow path forming substrate 31 in the Z1 direction, for example, by adhesive.

[0022] The channel-forming substrate 31 forms channels through which the ink flows. Specifically, the channel-forming substrate 31 has a space Ra, an intermediate liquid chamber Rb, a plurality of supply channels 312, and a plurality of communication channels 314. Space Ra is an elongated opening formed along the Y-axis. Each of the supply channels 312 and communication channels 314 is a through-hole formed for each nozzle N. Each communication channel 314 overlaps a corresponding nozzle N in a plan view from the Z1 direction. The intermediate liquid chamber Rb is an elongated space formed along the Y-axis across multiple nozzles N, and connects space Ra and the plurality of supply channels 312 to each other. A pressure chamber substrate 32 is bonded to the Z2 direction surface of the channel-forming substrate 31 with adhesive.

[0023] Multiple pressure chambers C1 are formed in the pressure chamber substrate 32. Ink ejected from the nozzle N is stored in the pressure chamber C1. The pressure chamber C1 is located between the nozzle plate 37 and the diaphragm 33 and is a space formed by the inner wall surface 32a of the pressure chamber substrate 32. A pressure chamber C1 is formed for each nozzle N. The pressure chamber C1 is an elongated space and extends in the X1 direction. Multiple pressure chambers C1 are arranged along the Y axis. Each pressure chamber C1 communicates with the communication channel 314 and the supply channel 312. Therefore, the pressure chamber C1 communicates with the nozzle N via the communication channel 314 and with the space Ra via the supply channel 312 and the intermediate liquid chamber Rb.

[0024] The nozzle plate 37, the channel-forming substrate 31, and the pressure chamber substrate 32 are manufactured by processing a silicon (Si) single crystal substrate using semiconductor manufacturing technologies such as photolithography and etching. However, known materials and manufacturing methods can be arbitrarily used for the manufacture of the nozzle plate 37, the channel-forming substrate 31, and the pressure chamber substrate 32.

[0025] The diaphragm 33 is connected to the surface of the pressure chamber substrate 32 opposite to the flow path forming substrate 31. The diaphragm 33 is positioned on the pressure chamber C1 and is elastically deformable. The diaphragm 33 is a plate-like member formed in a long rectangular shape along the Y-axis in a plan view. The diaphragm 33 and the pressure chamber may be an integrated structure, or they may be separate structures joined together with an adhesive or the like.

[0026] A piezoelectric element 5 is formed on the surface of the diaphragm 33 opposite to the pressure chamber C1. A piezoelectric element 5 is provided for each pressure chamber C1. The piezoelectric element 5 is elongated in shape along the X-axis in a plan view. The piezoelectric element 5 is a driving element that is driven when a driving signal is applied, and it applies pressure to the ink in the pressure chamber C1.

[0027] The seal 35 is bonded to the diaphragm 33, for example, by adhesive. The seal 35 is a structure that protects the multiple piezoelectric elements 5 and reinforces the mechanical strength of the pressure chamber substrate 32 and the diaphragm 33. A recess is formed in the seal 35 on the surface facing the diaphragm 33. The multiple piezoelectric elements 5 are housed inside this recess. The seal 35 also has a space 353 through which the wiring board 40 is inserted.

[0028] The housing portion 36 is joined to the flow channel forming substrate 31, for example, by adhesive. The housing portion 36 is a case for storing ink supplied to a plurality of pressure chambers C1. The housing portion 36 is formed, for example, by injection molding of a resin material. The housing portion 36 has a space Rc, a supply port 361, and a space 362. The supply port 361 is a conduit through which ink is supplied from the liquid container 9 and communicates with space Rc. Space Rc communicates with space Ra of the flow channel forming substrate 31. The space composed of space Rc and space Ra functions as a liquid storage chamber R for storing ink supplied to the plurality of pressure chambers C1. 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 branches from the relay liquid chamber Rb to each supply flow channel 312 and is supplied in parallel to the plurality of pressure chambers C1. Also, space 362 overlaps with space 353 of the sealing body 35 in a plan view. The wiring board 40 is inserted through spaces 353 and 362.

[0029] The wiring board 40 is connected to the diaphragm 33. The wiring board 40 is a mounted component on which multiple wires are formed for electrically connecting the control unit 20 and the liquid discharge head 3. For example, a flexible substrate such as an FPC (Flexible Printed Circuit) or FFC (Flexible Flat Cable) is preferably used for the wiring board 40. A drive signal and a reference voltage for driving the piezoelectric elements 5 are supplied from the wiring board 40 to each piezoelectric element 5.

[0030] Furthermore, a vibration absorber 38 is bonded to the Z1-direction surface of the channel-forming substrate 31, for example, by an adhesive. The vibration absorber 38 is a flexible film that constitutes the wall surface of the space Ra and absorbs pressure fluctuations of the ink in the liquid storage chamber R.

[0031] In this liquid ejection head 3, when the piezoelectric element 5 is deflected and deformed by the application of voltage, the diaphragm 33 deflects and deforms, i.e., vibrates, in a 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. After the ink is ejected, the piezoelectric element 5 returns to its original position.

[0032] Furthermore, although the liquid discharge head 3 includes all the elements shown in Figure 3, the components of the liquid discharge head 3 do not necessarily have to include all of these elements, and may also include additional elements.

[0033] 1-3. Piezoelectric element 5 Figures 4 and 5 are cross-sectional views showing the piezoelectric element 5 in Figure 3. The cross-section shown in Figure 4 is parallel to the YZ plane. The cross-section shown in Figure 5 is parallel to the XZ plane.

[0034] As shown in Figures 4 and 5, 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 a direction along the Z-axis, which is the stacking direction. Furthermore, as will be described later, as shown in Figure 6, the piezoelectric element 5 further comprises a first hydrogen absorption layer 54 and a second hydrogen absorption layer 55. 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 will be 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".

[0035] As shown in Figures 4 and 5, the lower electrodes 51 are provided above the diaphragm 33. The lower electrodes 51 are individual electrodes provided for each piezoelectric element 5. A drive signal with fluctuating voltage is applied to the lower electrodes 51. The lower electrodes 51 are elongated along the X-axis. Multiple lower electrodes 51 are arranged along the Y-axis with spacing between them. The lower electrodes 51 contain a conductive material.

[0036] The piezoelectric layer 53 is provided above the lower electrode 51. The piezoelectric layer 53 is, for example, a strip-shaped dielectric film that is continuous along the Y-axis across multiple piezoelectric elements 5. The piezoelectric layer 53 is, for example, a strip extending along the Y-axis and is separated for each piezoelectric element 5 by the formation of multiple notches. The piezoelectric layer 53 is, for example, made of a perovskite-type composite oxide.

[0037] The upper electrode 52 is provided above the piezoelectric layer 53. The upper electrode 52 is a strip-shaped common electrode that extends along the Y-axis so as to be continuous across multiple piezoelectric elements 5. A predetermined reference voltage is applied to the upper electrode 52. The upper electrode 52 contains a conductive material.

[0038] A voltage equivalent to the difference between the reference voltage applied to the upper electrode 52 and the drive signal corresponding to the discharge amount supplied to the lower electrode 51 is applied to the piezoelectric layer 53. The piezoelectric layer 53 deforms as a result of the voltage applied between the lower electrode 51 and the upper electrode 52, causing the piezoelectric element 5 to bend and deform, i.e., vibrate.

[0039] The diaphragm 33 vibrates when driven by the piezoelectric element 5. In the illustrated example, the diaphragm 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 positioned 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 made of an elastic material such as zirconium oxide (ZrO). x It is formed of an insulating material such as ). The first vibrating body layer 331 is formed, for example, by thermal oxidation of a part of the pressure chamber substrate 32. The second vibrating body layer 332 is formed, for example, by known film deposition techniques such as sputtering. The diaphragm 33 may consist of one layer or three or more layers.

[0040] Figure 4 illustrates the neutral axis A1 of the diaphragm 33. The neutral axis A1 is the position where the compressive force and contractile force are balanced, and where the stress in the axial direction along the X-Y plane of the diaphragm 33 is 0 (zero).

[0041] As shown in Figure 5, two conductors 381 and 382 are arranged on the upper electrode 52. Each of the conductors 381 and 382 is a strip-shaped conductive film positioned 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 electrically low-resistance conductive materials such as gold. Conductors 381 and 382 suppress the voltage drop of the reference voltage at the upper electrode 52. Conductors 381 and 382 also function as weights that define the vibration region of the diaphragm 33. Conductors 381 and 382 may be omitted.

[0042] Furthermore, a connecting wire 380 is connected to one end of the lower electrode 51 in the longitudinal direction along the X-axis. The lower electrode 51 is electrically connected to the wiring board 40 via the connecting wire 380. The upper electrode 52 is electrically connected to the aforementioned wiring board 40 via wiring etc., which is not shown in the figure.

[0043] Furthermore, in this embodiment, the lower electrode 51 is an individual electrode and the upper electrode 52 is a common electrode, but the lower electrode 51 may be a common electrode and the upper electrode 52 may be an individual electrode.

[0044] Figure 6 is a schematic diagram of the piezoelectric element 5 shown in Figure 4. As described above, the piezoelectric element 5 has a lower electrode 51, a piezoelectric layer 53, an upper electrode 52, a first hydrogen absorption layer 54, and a second hydrogen absorption layer 55. Each of the lower electrode 51, the piezoelectric layer 53, and the upper electrode 52 is composed of multiple layers. In this embodiment, the first hydrogen absorption layer 54 is placed between the lower electrode 51 and the piezoelectric layer 53. The second hydrogen absorption layer 55 is placed between the multiple layers that make up the piezoelectric 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 each correspond to a "hydrogen absorption layer".

[0045] The lower electrode 51 has a first electrode layer 511 and a second electrode layer 512. The first electrode layer 511 is positioned above the diaphragm 33 and is in contact with the diaphragm 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 to 120 nm.

[0046] The second electrode layer 512 is positioned between the first electrode layer 511 and the first hydrogen absorption layer 54 and is in contact with them. 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 be greater than or equal to the thickness of the first electrode layer 511.

[0047] In this embodiment, the lower electrode 51 is composed of two layers, but it may be composed of one layer or three or more layers. Furthermore, the first electrode layer 511 and the second electrode layer 512 may be composed of any conductive material, and may be composed of materials other than those mentioned above.

[0048] The first hydrogen absorption layer 54 is a "hydrogen absorption layer." The first hydrogen absorption layer 54 is provided above the lower electrode 51 and between the lower electrode 51 and the piezoelectric layer 53, in the direction along the Z-axis, which is the stacking direction of the piezoelectric element 5. The first hydrogen absorption layer 54 has the function of absorbing hydrogen. With the piezoelectric element 5 having such a first hydrogen absorption layer 54, it is possible to absorb hydrogen present at the interface between the lower electrode 51 and other layers, hydrogen present in the piezoelectric layer 53, or hydrogen that may enter the piezoelectric layer 53.

[0049] In Figure 6, the interface between the first hydrogen absorption layer 54 and the piezoelectric layer 53 is clearly depicted, but it does not need to be clearly shown. For example, a portion of the first hydrogen absorption layer 54 may be embedded in, dispersed in, or integrated with the piezoelectric layer 53. Also, the composition within the first hydrogen absorption layer 54 may be constant or graded. Therefore, the composition of the first hydrogen absorption layer 54 may differ between the piezoelectric layer 53 side and the lower electrode 51 side. Furthermore, the thickness of the first hydrogen absorption layer 54 along the Z-axis is not particularly limited, but for example, it is between 2 nm and 20 nm. Also, the first hydrogen absorption layer 54 may be composed of multiple layers.

[0050] The piezoelectric layer 53 is a laminate in which the first layer 531, the second layer 532, the third layer 533, the fourth layer 534, the fifth layer 535, and the sixth layer 536 are stacked in this order. The number of layers in the piezoelectric layer 53 is not limited to six, and may be five or fewer, or seven or more. However, by having multiple layers rather than a single layer, it is possible to form a piezoelectric layer 53 with excellent piezoelectric properties.

[0051] Each layer constituting the piezoelectric layer 53 is made of a perovskite-type composite oxide. More specifically, each layer is made of lead zirconate titanate (PZT:Pb(Zr,Ti)O3). The piezoelectric layer 53 may also contain at least one of the following elements: vanadium (V), niobium (Nb), tantalum (Ta), nickel (Ni), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi).

[0052] Furthermore, the thickness of each layer of the piezoelectric layer 53 is not particularly limited, but for example, it is between 90 nm and 250 nm.

[0053] The first layer 531 is positioned between the first hydrogen absorption layer 54 and the second hydrogen absorption layer 55 and is in contact with them. The second hydrogen absorption layer 55 is positioned between the first layer 531 and the second layer 532 and is in contact with them.

[0054] The second hydrogen absorption layer 55 has the function of absorbing hydrogen present in each layer or between layers that constitute 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.

[0055] In Figure 6, the interface between the second hydrogen absorption layer 55 and the second layer 532, and the interface between the second hydrogen absorption layer 55 and the first layer 531 are clearly depicted, but they do not necessarily have to be. For example, a portion of the second hydrogen absorption layer 55 may be embedded in, dispersed in, or integrated with the first layer 531 or the second layer 532. Also, the composition within the second hydrogen absorption layer 55 may be constant or gradient. Therefore, the composition of the second hydrogen absorption layer 55 may differ on the second layer 532 side and the first layer 531 side. Furthermore, the thickness of the second hydrogen absorption layer 55 along the Z axis is not particularly limited, but for example, it is between 2 nm and 20 nm. 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 it may be greater than or equal to the film thickness of the first hydrogen absorption layer 54. Also, the second hydrogen absorption layer 55 may be composed of multiple layers.

[0056] The upper electrode 52 is a structure in which the third electrode layer 521, the fourth electrode layer 522, the fifth electrode layer 523, and the third hydrogen absorption layer 524 are stacked in this order. The third electrode layer 521 is positioned above the piezoelectric layer 53 and is in contact with the sixth layer 536 of the piezoelectric layer 53. The third electrode layer 521 is made of, for example, iridium oxide (IrO x ) is included. The thickness of the third electrode layer 521 along the Z axis is not particularly limited, but for example, it is 5 nm or more and 20 nm or less. The fourth electrode layer 522 is for example titanium oxide (TiO x The fourth electrode layer 522 contains iridium (Ir). The thickness of the fourth electrode layer 522 along the Z-axis is not particularly limited, but is, for example, 2 nm to 20 nm. The fifth electrode layer 523 contains iridium (Ir), for example. The thickness of the fifth electrode layer 523 along the Z-axis is not particularly limited, but is, for example, 5 nm to 50 nm.

[0057] The third hydrogen absorption layer 524 is a "hydrogen absorption layer." The third hydrogen absorption layer 524 is provided on the upper electrode 52 side of the piezoelectric layer 53 and is located at the topmost 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, it is possible to suppress the intrusion of hydrogen into the piezoelectric layer 53 from the upper electrode 52 side compared to when it is not provided. In addition, it is possible to reduce the hydrogen content of each of the third electrode layers 521 to the fifth electrode layers 523.

[0058] The thickness of the third hydrogen absorption layer 524 along the Z-axis is not particularly limited, but is, for example, 5 nm to 20 nm. The third hydrogen absorption layer 524 has the function of absorbing hydrogen present in each layer or between layers constituting the piezoelectric element 5. In particular, the third hydrogen absorption layer 524 preferably absorbs hydrogen in the upper electrode 52. The composition of the third hydrogen absorption layer 524 may be constant or gradient within the layer. Furthermore, it may be formed from multiple layers.

[0059] In the example shown in Figure 6, an orientation control layer for controlling the orientation of the piezoelectric layer 53 is not provided between the first hydrogen absorption layer 54 and the piezoelectric layer 53, but such an orientation control layer may be provided. Furthermore, the first hydrogen absorption layer 54 may also have the function of such an orientation control layer. Because the first hydrogen absorption layer 54 has the function of such an orientation control layer, there is no need to provide a separate orientation control layer, thus simplifying manufacturing. The orientation control layer, for example, preferentially orients the crystals in the upper layers to a predetermined plane orientation, or adjusts the degree of orientation to a predetermined plane orientation.

[0060] Similarly, although an orientation control layer for controlling the orientation of the second layer 532 is not provided between the second hydrogen absorption layer 55 and the second layer 532, such an orientation control layer may be provided. The second hydrogen absorption layer 55 may have the function of such an orientation control layer. However, since the second hydrogen absorption layer 55 has the function of such an orientation control layer, there is no need to provide a separate orientation control layer, making manufacturing easier.

[0061] 1-4. Piezoelectric layer As described above, the piezoelectric layer 53 consists of multiple layers. The piezoelectric layer 53 is sandwiched between a pair of electrodes, the lower electrode 51 and the upper electrode 52. The multiple layers constituting the piezoelectric layer 53 have a "central layer". In this embodiment, the "central layer" is the third layer 533 or the fourth layer 534. The "central layer" is a layer located in or near the center of the piezoelectric layer 53, which is not in contact with the upper electrode 52 and the lower electrode 51 located above and below the piezoelectric layer 53, and is a layer sandwiched between the other layers of the piezoelectric layer 53. Note that when the piezoelectric layer consists of three or more layers, the layer located in or near the center of the piezoelectric layer 53 corresponds to the "central layer".

[0062] The following explanation will focus on the case where the "central layer" is the third layer 533. The rate of change ΔH of the hydrogen content in the third layer 533 is 21% or less. 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)). H(Ave) is the average hydrogen content in layer 533. H(max) is the maximum hydrogen content in layer 533. H(min) is the minimum hydrogen content in layer 533. H(Ave), H(max), and H(min) are measured, for example, by secondary ion mass spectrometry. The rate of change ΔH of the hydrogen content in the third layer 533, which is the "central layer," is 21% or less. This suppresses the deterioration of the displacement characteristics of the piezoelectric element compared to when ΔH exceeds 21%.

[0063] The hysteresis characteristics of the piezoelectric element 5 change over time depending on the hydrogen content of the piezoelectric layer 53, deviating significantly from the design stage. As a result, the displacement characteristics of the piezoelectric element 5 decrease over time. Furthermore, the amount of displacement obtained from the drive voltage value set at the design stage changes. When the piezoelectric layer 53 is formed from multiple layers, the decrease in displacement characteristics was particularly pronounced. As will be described later, the piezoelectric layer 53 is formed by repeatedly depositing and firing each of the multiple layers. It is thought that hydrogen enters the piezoelectric layer 53 during this manufacturing process, changing the hydrogen content of the piezoelectric layer 53. Moreover, when comparing multiple piezoelectric elements 5, even when the composition gradient of the piezoelectric layer 53 was the same, a decrease in the displacement characteristics of the piezoelectric element 5 was observed depending on the hydrogen content.

[0064] As a result of their intensive research, the inventors discovered that by keeping the rate of change ΔH of the hydrogen content in the third layer 533, which is the central layer of the piezoelectric body layer 53, small, the deterioration of the displacement characteristics of the piezoelectric element 5 over time can be suppressed. Specifically, if the rate of change ΔH is 21% or less, the deterioration of the displacement characteristics of the piezoelectric element 5 can be suppressed. Furthermore, since the deterioration of the displacement characteristics of the piezoelectric element 5 can be suppressed from the design stage, there is no need to adjust the difference by changing the drive voltage or waveform in accordance with the changes over time, thus improving usability.

[0065] The central layer of the piezoelectric layer 53 significantly affects the displacement characteristics of the piezoelectric element 5. For example, it is thought that the performance of the piezoelectric element 5 improves as the range of the layer away from the neutral axis A1 of the piezoelectric layer 53 increases. By keeping the rate of change ΔH of the hydrogen content in the central layer small, it is thought that the rate of change of the hydrogen content in the other layers, and furthermore, the average hydrogen content in the piezoelectric layer 53, can be reduced.

[0066] Furthermore, since the central layer is a layer that does not contact the upper electrode 52 and the lower electrode 51, and is sandwiched between the other layers of the piezoelectric layer 53, the amount of hydrogen can be measured while suppressing the influence from the upper electrode 52 and the lower electrode 51. For example, when measuring a layer that is in contact with the upper electrode 52 or the lower electrode 51 using secondary ion mass spectrometry, the measurement may be unstable due to the influence of the interface between the upper electrode 52 or the lower electrode 51 and the layer. In other words, the secondary ion intensity near the interface may change significantly due to the interfacial effect. By measuring the central layer that is not in contact with the upper electrode 52 and the lower electrode 51, the amount of hydrogen can be measured while suppressing the influence from the upper electrode 52 and the lower electrode 51.

[0067] By keeping the rate of change ΔH of the hydrogen content in the third layer 533 to 21% or less, it is possible to suppress large differences in displacement between multiple piezoelectric elements 5. Therefore, it is possible to eliminate the need to change the drive voltage and waveform for each piezoelectric element 5 in order to adjust for the difference in displacement between multiple piezoelectric elements 5. Thus, the usability of the piezoelectric elements 5 can be improved.

[0068] Furthermore, in this embodiment, the rate of change ΔH in the fourth layer 534 is 21% or less, similar to the rate of change ΔH in the third layer 533. However, if either the rate of change ΔH in the fourth layer 534 or the rate of change ΔH in the fourth layer 534 is 21% or less, the decrease in the displacement characteristics of the piezoelectric element 5 can be suppressed compared to the case where it exceeds 21%.

[0069] Furthermore, the rate of change ΔH of the hydrogen content in the third layer 533 mentioned above should be 21% or less, but it is more preferable that it be 16% or less. By keeping the rate of change ΔH at 16% or less, the deterioration of the displacement characteristics of the piezoelectric element 5 can be suppressed more effectively compared to when it exceeds 16%.

[0070] The rate of change ΔH in the fourth layer 534 is preferably 16% or less, similar to the rate of change ΔH in the third layer 533. However, if either the rate of change ΔH in the fourth layer 534 or the rate of change ΔH in the fourth layer 534 is 16% or less, the decrease in the displacement characteristics of the piezoelectric element 5 can be suppressed compared to the case where it exceeds 16%.

[0071] Furthermore, it is preferable that the hydrogen content in the lower part of the third layer 533 is greater than the hydrogen content in the upper part of the third layer 533. In other words, in the third layer 533, the hydrogen content is low at positions away from the neutral axis A1 of the piezoelectric layer 53. This makes it possible to suppress a decrease in the displacement characteristics of the piezoelectric element 5.

[0072] Similarly, it is preferable that the hydrogen content of the lower part of the fourth layer 534 is greater than the hydrogen content of the upper part of the fourth layer 534. However, in the third layer 533 and the fourth layer 544, the hydrogen content of the lower part may be less than or equal to the hydrogen content of the upper part. The lower part of a layer refers to the portion located in the Z1 direction. For example, it refers to the range from the bottom surface in the Z1 direction of the layer to 25 nm in the Z2 direction. Similarly, the upper part of a layer refers to the portion located in the Z2 direction of the layer. For example, it refers to the range from the top surface in the Z2 direction of the layer to 25 nm in the Z1 direction. The hydrogen content in these ranges is measured, for example, using secondary ion mass spectrometry.

[0073] Furthermore, the film thickness D3 of the third layer 533, which is the central layer of the multiple layers constituting the piezoelectric layer 53, is not particularly limited, but is preferably 100 nm or more and 300 nm or less.

[0074] As will be described later, the manufacturing process for the piezoelectric layer 53 may include a degreasing process and a firing process. In this case, there is a risk that hydrogen may not be completely removed from the precursors of each layer constituting the piezoelectric layer 53 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, there is a high possibility that hydrogen will not be completely removed. By setting the film thickness D3 to 100 nm or more and 300 nm or less, compared to cases outside this range, hydrogen can be removed more easily during the degreasing process, and the firing process time can be shortened to make it more difficult for hydrogen to enter.

[0075] Similarly, the film thickness D4 of the fourth layer 534, which is the central layer of the multiple layers constituting the piezoelectric layer 53, is not particularly limited, but is preferably 100 nm or more and 300 nm or less.

[0076] Furthermore, when the piezoelectric layer 53 is made of a perovskite-type composite oxide containing Ti, the rate of change ΔTi of the titanium content in the third layer 533 is preferably 13% or less. 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)). Ti(Ave) is the average titanium content in the third layer 533. Ti(max) is the maximum titanium content in the third layer 533. Ti(min) is the minimum titanium content in the third layer 533. Ti(Ave), Ti(max), and Ti(min) are measured, for example, by secondary ion mass spectrometry.

[0077] The compositional gradient of titanium in the piezoelectric layer 53 affects the displacement characteristics of the piezoelectric element 5. By keeping the rate of change ΔTi of the third layer 533, the central layer of the piezoelectric layer 53, at 13% or less, the compositional gradient of titanium in the piezoelectric layer 53 is suppressed compared to the case where it exceeds 13%. Therefore, the displacement characteristics of the piezoelectric element 5 can be improved. Furthermore, titanium has high hydrogen storage capacity. Consequently, if there is a large variation in the titanium content, there will be a large variation in the hydrogen content in the piezoelectric layer 53. Therefore, by suppressing the variation in the titanium content, the variation in the hydrogen content can be suppressed. As a result, the decrease in the displacement characteristics of the piezoelectric element 5 can be suppressed.

[0078] The rate of change ΔTi in the fourth layer 534 is preferably 13% or less, similar to the rate of change ΔTi in the third layer 533. However, if either the rate of change ΔTi in the fourth layer 534 or the rate of change ΔTi in the fourth layer 534 is 13% or less, the decrease in the displacement characteristics of the piezoelectric element 5 can be suppressed compared to the case where it exceeds 13%.

[0079] Furthermore, the first hydrogen absorption layer 54 and the third hydrogen absorption layer 524 each correspond to a "hydrogen absorption layer." The first hydrogen absorption layer 54 and the third hydrogen absorption layer 524 are provided at positions that sandwich the piezoelectric layer 53 in the stacking direction of the multiple layers constituting the piezoelectric layer 53. The piezoelectric layer 53 is provided between the first hydrogen absorption layer 54 and the third hydrogen absorption layer 524.

[0080] The amount of hydrogen in the piezoelectric layer 53 increases due to its generation during the degreasing and calcination of the precursor, as well as its intrusion from outside 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 when they are not provided.

[0081] Furthermore, in this embodiment, a second hydrogen absorption layer 55 is provided. This allows for a further reduction in the hydrogen content of the piezoelectric layer 53.

[0082] Furthermore, the first hydrogen absorption layer 54 is composed 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 depending on temperature or pressure. When the first hydrogen absorption layer 54 absorbs hydrogen, hydrogen penetrates into the gaps 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 containing such metals, or compounds. The first hydrogen absorption layer 54 is composed of, for example, titanium or lead titanate (PbTiO3). Alternatively, the first hydrogen absorption layer 54 may be composed of, for example, a composite oxide containing bismuth (Bi), iron (Fe), titanium (Ti), and lead (Pb).

[0083] Furthermore, the second hydrogen absorption layer 55 and the third hydrogen absorption layer 524 each similarly contain a hydrogen storage material that can combine with hydrogen to form a hydride.

[0084] Furthermore, as mentioned above, the piezoelectric layer 53 is composed of lead zirconate titanate (PZT), a perovskite-type composite oxide. The fact that the piezoelectric layer 53 is made of PZT is particularly effective in suppressing the change in the hysteresis characteristics of the piezoelectric element 5 caused by the provision of the first hydrogen absorption layer 54.

[0085] Furthermore, it is particularly preferable that each of the first hydrogen absorption layer 54, the second hydrogen absorption layer 55, and the third hydrogen absorption layer 524 contains titanium. Moreover, it is preferable that each of these layers is made of titanium. Titanium has excellent hydrogen absorption performance. Therefore, by including titanium in these layers, more hydrogen that might penetrate the piezoelectric layer 53 can be absorbed compared to when titanium is not included.

[0086] Figure 7 is a table showing examples and comparative examples. Figure 7 shows Examples 1-10 and Comparative Examples 1-6. Each of Examples 1-10 and Comparative Examples 1-6 has six piezoelectric layers 53. The thickness of each piezoelectric layer 53 is approximately 220 nm. Figure 7 also shows the results and evaluations of the hydrogen content, rate of change ΔTi, and ΔH in the third layer 533, measured and calculated by secondary ion mass spectrometry. Similar results and evaluation trends were obtained for the fourth layer 534.

[0087] Each piezoelectric layer 53 in Examples 1 to 10 is composed of lead zirconate titanate, a perovskite-type composite oxide containing Ti. Furthermore, Examples 1 to 10 and Comparative Examples 1 to 6 differ in the hydrogen content and concentration in the third layer 533. The hydrogen concentration in the third layer 533 was adjusted by varying the heating conditions in the manufacturing method and the amount of hydrogen in the hydrogen absorption layer. In addition to the examples shown in Figure 7 and the piezoelectric element 5 shown in Figure 6, examples of configurations shown in the modified examples described later are also included. The first modified example described later corresponds to Example 9, and the second modified example described later corresponds to Example 10.

[0088] As shown in Figure 7, in Examples 1 to 10, the rate of change ΔH of the hydrogen content in the third layer 533 is 21% or less, whichever is greater of (H(max)-H(ave)) / H(ave)) or (H(min)-H(ave)) / H(ave)). On the other hand, in Comparative Examples 1 to 6, the rate of change ΔH of the hydrogen content in the third layer 533 is 21% or less, whichever is greater of (H(max)-H(ave)) / H(ave)) or (H(min)-H(ave)) / H(ave)).

[0089] Each embodiment exhibits superior displacement characteristics compared to each comparative example. The evaluation is based on the rate of change in the displacement of the piezoelectric element 5 over time. A durability test was conducted in which a predetermined drive pulse was continuously applied 10 billion times to a liquid discharge head equipped with the piezoelectric element 5, and the rate of decrease in the displacement of the piezoelectric element 5 over time before and after the application of the predetermined drive pulse was determined. The predetermined drive pulse is a trapezoidal waveform with a voltage of 25V and a frequency of 100Hz. An evaluation of "〇" indicates that the rate of change in displacement over time is less than -5.0%. An evaluation of "◎" indicates that the rate of change over time is less than -3.0%.

[0090] As mentioned above, the rate of change ΔH for Examples 1 to 10 is less than 21%, while the rate of change ΔH for Comparative Examples 1 to 6 exceeds 21%. Therefore, each example exhibits a lower rate of displacement change over time for the piezoelectric element 5 compared to each comparative example. Consequently, Examples 1 to 10 can suppress the displacement change over time for the piezoelectric element 5 compared to Comparative Examples 1 to 6. As a result, Examples 1 to 10 can suppress the deterioration of the displacement characteristics of the piezoelectric element. Therefore, the liquid discharge head 3 equipped with the piezoelectric element 5 of Examples 1 to 10 can exhibit excellent discharge characteristics.

[0091] Furthermore, in Examples 1, 2, 5, and 7-10, the rate of change ΔH of the hydrogen content in the third layer 533 is 16% or less. In Examples 1, 2, 5, and 7-10, the rate of change over time is less than -3.0%, indicating a very small rate of change over time. Therefore, Examples 1, 2, 5, and 7-10 can achieve higher displacement characteristics of the piezoelectric element 5 compared to the other examples. Thus, the liquid discharge heads equipped with the piezoelectric element 5 in Examples 1, 2, 5, and 7-10 can exhibit particularly excellent discharge characteristics.

[0092] Furthermore, in Examples 1 to 10, the rate of change ΔTi of the titanium content in the third layer 533 is 13% or less. Although not shown in Figure 7, the film thickness D3 of the third layer 533 is approximately 220 nm. In addition, the piezoelectric element 5 in Examples 1 to 10 has a first hydrogen absorption layer 54 and a third hydrogen absorption layer 524.

[0093] Figure 8 shows the measurement results of the piezoelectric element 5 of Example 1 using a secondary ion mass spectrometer (SIMS). Figure 9 shows the measurement results of the piezoelectric element 5 of Example 2 using a secondary ion mass spectrometer. Figure 10 shows the measurement results of the piezoelectric element 5 of Comparative Example 1 using a secondary ion mass spectrometer. Figure 11 shows the measurement results of the piezoelectric element 5 of Comparative Example 2 using a secondary ion mass spectrometer.

[0094] 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. Furthermore, Examples 2, and Comparative Examples 1 and 2 have a protective film 6 as shown in the third modified example described later.

[0095] In Figures 8-11, the horizontal axis represents depth [nm]. Since the analysis was performed in the Z1 direction from the upper electrode 52, the shallower depths represent the upper electrode 52 side, and the deeper depths represent the lower electrode 51 side. The vertical axis in Figures 8-11 shows the hydrogen concentration [atoms / cc]. This hydrogen concentration was determined using standard samples doped with the target element at known concentrations. For titanium and zirconium, the ionic intensity is shown. Note that "E" represents a power of 10. For example, 1E+20 is 1 × 10⁻¹⁰. 20 This represents 1E+19, which is 1 × 10 19 It represents.

[0096] Furthermore, although clear line segments are drawn along the interfaces of each layer in Figures 8-11, the position of the interfaces may vary slightly depending on the criteria used. Also, due to SIMS measurement errors and interface effects, the peak position may shift relative to, for example, the depth at which the first hydrogen absorption layer 54 and the second hydrogen absorption layer 55 are located. In this case, for example, the hydrogen peak observed near the depth at which the first hydrogen absorption layer 54 and the second hydrogen absorption layer 55 are located is considered to be the peak value at the first hydrogen absorption layer 54 and the second hydrogen absorption layer 55.

[0097] Figures 8-11 show H(max), H(min), Ti(max), and Ti(min). The first example in Figure 8 and the second example in Figure 9 show smaller changes in the hydrogen content ΔH in the third layer 533 compared to the first comparative example in Figure 10 and the second comparative example in Figure 11. Similarly, the first example in Figure 8 and the second example in Figure 9 show smaller changes in the titanium content ΔTi in the third layer 533 compared to the first comparative example in Figure 10 and the second comparative example in Figure 11. Note that in Figures 8-11, Ti is shown as secondary ionic strength. The average hydrogen (H) and titanium (Ti) content of each layer was calculated by averaging the hydrogen and titanium content from the interface at one end of the layer to the interface at the other end.

[0098] Furthermore, in both the first embodiment shown in Figure 8 and the second embodiment shown in Figure 9, the hydrogen content of the lower part of the third layer 533 is greater than the hydrogen content of the upper part of the third layer 533. Note that the lower part is the deeper part, and the upper part is the shallower part.

[0099] 1-5. Manufacturing method of piezoelectric element 5 Figure 12 is a diagram showing the flow of the manufacturing method for the piezoelectric element 5 shown in Figure 6. As shown in Figure 12, the manufacturing method for the piezoelectric element 5 includes a lower electrode formation step S11, an intermediate layer formation step S12, and an upper electrode formation step S13. These steps are performed in this order.

[0100] In the lower electrode formation step S11, the 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, first, for example, the first electrode layer 511 is formed by depositing a layer containing a conductive material such as platinum on the diaphragm 33 using sputtering, vapor deposition, or CVD (Chemical Vapor Deposition). Next, for example, the second electrode layer 512 is formed by depositing a layer containing a conductive material such as iridium on the first electrode layer 511 using sputtering, vapor deposition, or CVD.

[0101] The intermediate layer formation step S12 includes the formation of a first hydrogen absorption layer 54, a piezoelectric layer 53, and a second hydrogen absorption layer 55. Specifically, first, 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 made of a perovskite-type composite oxide such as PZT is formed on the layer containing the hydrogen storage material using the sol-gel method and then degreased. Next, the layer containing the hydrogen storage material and the first layer precursor are fired. As a result, the first hydrogen absorption layer 54 and the first layer 531 are formed.

[0102] Next, another layer containing a hydrogen storage material such as titanium is deposited on the first layer 531 using sputtering, vapor deposition, or CVD. Then, a second layer precursor made of a perovskite-type composite oxide such as PZT is deposited on the other layer containing the hydrogen storage material using the sol-gel method and degreased. Next, the other layer containing the hydrogen storage material and the second layer precursor are calcined. As a result, the second hydrogen absorption layer 55 and the second layer 532 are formed.

[0103] When forming the second hydrogen absorption layer 55, there is a risk that moisture may remain on the surface of the first layer 531 during the formation of the second hydrogen absorption layer 55. For this reason, it is preferable to perform a heating step to remove surface moisture during the formation of the second hydrogen absorption layer 55. This reduces the amount of moisture remaining on the surface of the first layer 531. As a result, the amount of hydrogen absorbed by the second hydrogen absorption layer 55 is reduced during its formation, allowing the second hydrogen absorption layer 55 to absorb hydrogen sufficiently after formation.

[0104] Next, a third layer precursor made of a perovskite-type composite oxide such as PZT is deposited on the second layer 532 using the sol-gel method, and then the third layer precursor is calcined. This forms the third layer 533. The fourth layer 534, fifth layer 535, and sixth layer 536 are formed by the same method. 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 calcined together.

[0105] 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 smaller 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, which is the middle layer of the piezoelectric layer 53, during the sol-gel film formation stage.

[0106] In the upper electrode formation step S13, the upper electrode 52 is formed. The upper electrode formation step 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, a third electrode layer 521 containing a metal oxide is formed on the sixth layer 536 by sputtering, vapor deposition, or CVD, followed by firing. Next, a fourth electrode layer 522 containing a metal oxide is formed on the third electrode layer 521 by sputtering, vapor deposition, or CVD, followed by firing.

[0107] Next, a fifth electrode layer 523 is formed on the fourth electrode layer 522 by depositing a layer containing a conductive material such as iridium using sputtering, vapor deposition, or CVD. Then, a third hydrogen absorption layer 524 is formed on the fifth electrode layer 523 by depositing a layer containing a hydrogen storage material such as titanium using sputtering, vapor deposition, or CVD. The piezoelectric element 5 is thus manufactured.

[0108] 2. Variations The embodiments illustrated above can be modified in various ways. Specific examples of modifications that can be applied to the aforementioned embodiments are given below. Two or more embodiments arbitrarily selected from the following examples can be combined as appropriate, to the extent that they do not contradict each other.

[0109] 2-1. First variation Figure 13 is a schematic diagram of the piezoelectric element 5A of the first modified example. As shown in Figure 13, the first hydrogen absorption layer 54A of the piezoelectric element 5A of the first modified example consists 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 that mainly constitutes the first absorption layer 541. The first absorption layer 541 is made of titanium, for example. The second absorption layer 542 is made of lead zirconate (PbZrO3) or lead titanate (PbTiO3), for example. The main constituent material refers to a material that makes up 50% or more of the materials constituting the layer.

[0110] Since the first hydrogen absorption layer 54A is composed of multiple layers, the penetration of hydrogen into the piezoelectric layer 53 can be suppressed more effectively compared to a single layer.

[0111] Furthermore, the first absorption layer 541 and the second absorption layer 542 may have different or the same hydrogen absorption performance, i.e., the amount of hydrogen absorbed. Also, the second absorption layer 542 may function as the orientation control layer described above.

[0112] In the first embodiment and the first modified example, a portion of the lower electrode 51 may be considered as part of the first hydrogen absorption layer 54, and in this case as well, the first hydrogen absorption layer 54 may be considered to consist of multiple layers. For example, the second electrode layer 512 of the lower electrode 51 may be considered as part of the first hydrogen absorption layer 54. Furthermore, the first hydrogen absorption layer 54 may also function as an electrode.

[0113] 2-2. Second variation Figure 14 is a cross-sectional view of the piezoelectric element 5 of the second modified example. As shown in Figure 14, a protective film 6 is placed on the upper surface of the piezoelectric layer 53. Specifically, the protective film 6 is placed on one end of the piezoelectric layer 53 along the X-axis. A portion of the upper surface of the piezoelectric layer 53 is not covered by the upper electrode 52 and is exposed. The protective film 6 is placed on this exposed portion. The protective film 6 includes, for example, ceramics such as aluminum oxide (AlOx) and silicon nitride.

[0114] The protective film 6 is provided on the exposed portion of the piezoelectric layer 53, thereby suppressing hydrogen from entering the piezoelectric layer 53. In addition, a portion of the protective film 6 is sandwiched between the upper electrodes 52. Specifically, the third electrode layer 521, the fourth electrode layer 522, and the fifth electrode layer 523 are arranged below the protective film 6. The third hydrogen absorption layer 524 is arranged above the protective film 6. A portion of the third hydrogen absorption layer 524 is provided on the third hydrogen absorption layer 524, so that the third hydrogen absorption layer 524 can absorb hydrogen in the protective film 6, thereby suppressing hydrogen in the protective film 6 from entering the piezoelectric layer 53.

[0115] The third hydrogen absorption layer 524 may be located below the protective film 6. Furthermore, while the third hydrogen absorption layer 524 is provided on a portion of the upper surface of the protective film 6, it may also be provided on the entire upper surface of the protective film 6.

[0116] Furthermore, if a protective film 6 is provided, in the manufacturing method of the piezoelectric element 5, the protective film 6 is formed between the formation of the third electrode layer 521, the fourth electrode layer 522, and the fifth electrode layer 523, and 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.

[0117] 2-3. Other variations The "liquid dispensing head" may be a circulating type head having a so-called circulation channel.

[0118] "Image forming apparatus" can be used not only in equipment dedicated to printing, but also in various other devices such as facsimile machines and photocopiers. The applications of image forming apparatus are not limited to printing. For example, an image forming apparatus that dispenses a colorant solution is used as a manufacturing apparatus to form color filters for display devices such as liquid crystal display panels. Also, an image forming apparatus that dispenses a conductive material solution is used as a manufacturing apparatus to form wiring and electrodes on a wiring board. Furthermore, an image forming apparatus that dispenses a solution of organic matter related to living organisms is used, for example, as a manufacturing apparatus to produce biochips.

[0119] Although the present invention has been described above based on preferred embodiments, the present invention is not limited to the embodiments described above. Furthermore, the configuration of each part of the present invention can be replaced with any configuration that performs a similar function to the embodiments described above, and any configuration can be added.

[0120] 3. Addendum From the above embodiments or modifications, for example, the following embodiments can be understood.

[0121] A piezoelectric element according to a first embodiment, which is a preferred example of the present disclosure, is a piezoelectric element having a piezoelectric layer consisting of a plurality of layers and a pair of electrodes arranged on either side of the piezoelectric layer, wherein the piezoelectric layer is composed of zirconate titanate, and when the average value H(Ave), maximum value H(max), and minimum value H(min) of the hydrogen content contained in the central layer of the plurality of layers are defined as H(max) - H(ave) / H(ave) or the larger of the absolute values ​​of (H(min) - H(ave)) / H(ave)) is defined as the rate of change of the hydrogen content, then ΔH is 21% or less.

[0122] According to this first embodiment, by having a rate of change ΔH of 21% or less, the decrease in the displacement characteristics of the piezoelectric element can be suppressed compared to the case where ΔH exceeds 21%.

[0123] In the piezoelectric element of the second embodiment, which is a preferred example of the first embodiment, the rate of change ΔH is 16% or less.

[0124] According to this second embodiment, by having a rate of change ΔH of 16% or less, the deterioration of the displacement characteristics of the piezoelectric element can be particularly suppressed compared to the case where ΔH exceeds 16%.

[0125] In a piezoelectric element of the third embodiment, which is a preferred example of the first or second embodiment, the hydrogen content on the lower side is greater than the hydrogen content on the upper side in the central layer of the plurality of layers.

[0126] By having a higher hydrogen content on the lower side than on the upper side, the decrease in the displacement characteristics of the piezoelectric element can be suppressed.

[0127] In the piezoelectric element of the fourth embodiment, which is a preferred example of the first or third embodiment, the thickness of the central layer of the plurality of layers is 100 nm or more and 300 nm or less.

[0128] The manufacturing process for a piezoelectric layer may include a degreasing process and a firing process. In this case, there is a risk that hydrogen may not be completely removed from the precursors of each layer constituting the piezoelectric layer during the degreasing process, or that hydrogen may enter the piezoelectric layer during the firing process. By setting the film thickness to 100 nm to 300 nm, compared to cases outside this range, hydrogen can be removed more easily during the degreasing process, and the firing time can be shortened to make it more difficult for hydrogen to enter.

[0129] In a piezoelectric element of the fifth embodiment, which is a preferred example of the first or fourth embodiment, the average value Ti(Ave) of the titanium content in the central layer of the plurality of layers is Ti(max), the maximum value is Ti(min), and the minimum value is Ti(min). When ΔTi is defined as the rate of change of titanium content, whichever is greater of (Ti(max)-Ti(ave)) / Ti(ave)) or (Ti(min)-Ti(ave)) / Ti(ave)), ΔTi is 13% or less.

[0130] The compositional gradient of titanium in the piezoelectric layer affects the displacement characteristics of the piezoelectric element. According to the fifth embodiment, since the rate of change ΔTi is 13% or less, the compositional gradient of titanium in the piezoelectric layer is suppressed compared to the case where it exceeds 13%, and thus the displacement characteristics can be improved. In addition, titanium has high hydrogen storage capacity. Therefore, if there is a large variation in the titanium content, there will be a large variation in the hydrogen content in the piezoelectric layer. Accordingly, by suppressing the variation in the titanium content, the variation in the hydrogen content can be suppressed. Thus, the decrease in displacement characteristics can be suppressed.

[0131] In the piezoelectric element of the sixth embodiment, which is a preferred example of the first or fifth embodiment, a hydrogen absorption layer is provided at a position sandwiching the piezoelectric layer in the stacking direction of the plurality of layers.

[0132] Hydrogen in the piezoelectric layer increases due to its generation during the degreasing and calcination of the precursor, as well as its intrusion from outside the piezoelectric element. By providing a hydrogen absorption layer, the hydrogen content in the piezoelectric layer can be reduced compared to when no hydrogen absorption layer is provided.

[0133] A preferred example of the liquid dispensing head of this disclosure has a piezoelectric element which is a preferred example of any of the first to sixth embodiments.

[0134] This allows us to provide a liquid discharge head with excellent displacement characteristics. [Explanation of Symbols]

[0135] 3...Liquid discharge head, 5...Piezoelectric element, 6...Protective film, 33...Diaphragm, 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 vibrator layer, 332...Second vibrator 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 axis, C1...Pressure chamber, N...Nozzle.

Claims

1. A piezoelectric element comprising a piezoelectric layer consisting of multiple layers, and a pair of electrodes arranged on either side of the piezoelectric layer, The piezoelectric layer is composed of zirconate titanate, Let H(Ave) be the average value of the hydrogen content in the central layer of the aforementioned multiple layers, H(max) be the maximum value, and H(min) be the minimum value. When ΔH is the greater of the absolute values ​​of (H(max) - H(ave)) / H(ave) or (H(min) - H(ave)) / H(ave)) as the rate of change of the hydrogen content, then ΔH is 21% or less. A piezoelectric element characterized by the following features.

2. In the piezoelectric element according to claim 1, The rate of change ΔH is 16% or less. A piezoelectric element characterized by the following features.

3. In the piezoelectric element according to claim 1, In the central layer of the aforementioned multiple layers, the hydrogen content on the lower side is greater than the hydrogen content on the upper side. A piezoelectric element characterized by the following features.

4. In the piezoelectric element according to any one of claims 1 to 3, The thickness of the central layer among the aforementioned multiple layers is between 100 nm and 300 nm. A piezoelectric element characterized by the following features.

5. In the piezoelectric element according to any one of claims 1 to 3, Let Ti(Ave) be the average value of the titanium content in the central layer of the aforementioned multiple layers, Ti(max) be the maximum value, and Ti(min) be the minimum value. When ΔTi is defined as the rate of change of titanium content, whichever is greater than (Ti(max) - Ti(ave)) / Ti(ave) or (Ti(min) - Ti(ave)) / Ti(ave)), then ΔTi is 13% or less. A piezoelectric element characterized by the following features.

6. In the piezoelectric element according to any one of claims 1 to 3, In the stacking direction of the plurality of layers, the hydrogen absorption layer is located between the piezoelectric layer. A piezoelectric element characterized by the following features.

7. Having the piezoelectric element described in claim 1, A liquid dispensing head characterized by the following features.

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