Piezoelectric element and liquid dispensing head

Abstract

To provide a liquid dispensing head capable of suppressing the outflow of adhesive onto the diaphragm. [Solution] The piezoelectric element is a piezoelectric element in which a lower electrode, a piezoelectric layer made of a perovskite-type composite oxide, and an upper electrode are stacked in the stacking direction, and the upper electrode has a first hydrogen absorption layer that absorbs hydrogen. Preferably, the upper electrode of the piezoelectric element has a second hydrogen absorption layer different from the first hydrogen absorption layer. Preferably, in the stacking direction, the thickness of the first hydrogen absorption layer is thicker than the thickness of the second hydrogen absorption layer.

Description

Technical Field

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

Background Art

[0002] 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 conventionally proposed. As the liquid ejection head, a head that discharges the liquid filled in the pressure chamber from the nozzle by vibrating a diaphragm constituting the 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 the 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, followed by firing the precursor film. By repeating the film formation and firing of the precursor film a plurality of times, a piezoelectric layer composed of a plurality of layers is formed.

[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, the inventors, through diligent research, have discovered that the hysteresis characteristics change significantly depending on the hydrogen content of the piezoelectric layer. In particular, they found that even piezoelectric elements with equivalent compositional gradients exhibit different hysteresis characteristics depending on the hydrogen content. They also found that hydrogen tended to enter from outside the piezoelectric layer.

[0008] When the hysteresis characteristics of a piezoelectric element change, differences in displacement occur for each piezoelectric element. Therefore, it is necessary to adjust for these differences by changing the driving voltage or waveform for each piezoelectric element. Consequently, this presents a problem in terms of usability. [Means for solving the problem]

[0009] A piezoelectric element according to a preferred embodiment of the present invention is a piezoelectric element in which a lower electrode, a piezoelectric layer made of a perovskite-type composite oxide, and an upper electrode are stacked in the stacking direction, wherein the upper electrode has a first hydrogen absorption layer that absorbs hydrogen.

[0010] A liquid dispensing head according to a preferred embodiment of the present invention has a piezoelectric element. [Brief explanation of the drawing]

[0011] [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] It is a cross-sectional view of the piezoelectric element shown in FIG. 3. [Figure 6] It is a diagram schematically showing the piezoelectric element shown in FIG. 4. [Figure 7] It is a diagram showing the measurement result of the secondary ion mass spectrometer (SIMS) of the piezoelectric element shown in FIG. 6. [Figure 8] It is a diagram showing the manufacturing process flow of the piezoelectric element of FIG. 6. [Figure 9] It is a diagram schematically showing the piezoelectric element of the first modification. [Figure 10] It is a diagram schematically showing the piezoelectric element of the second modification. [Figure 11] It is a cross-sectional view of the piezoelectric element of the third modification. [Figure 12] It is a diagram showing the measurement result of the secondary ion mass spectrometer of the piezoelectric element of the third modification. [Figure 13] It is a diagram schematically showing the piezoelectric element of the fourth modification.

MODE FOR CARRYING OUT THE INVENTION

[0012] [[ID=…]] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, the dimensions or scales of each part are appropriately different from the actual ones, and there are also parts schematically shown for easy understanding. Further, the scope of the present invention is not limited to these embodiments unless there is a description to specifically limit the present invention 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, and also includes a configuration 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 may be substantially equal, including manufacturing errors and the like. Also, "element α and element β are laminated" means that element α and element β may be arranged in the vertical direction, and it does not matter whether element α and element β are in direct contact or not.

[0013] 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 that are 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 for example, they may intersect at an angle within the range of 80° or more and 100° or less.

[0014] 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 replenishing ink is used as the liquid container 9.

[0015] The image forming apparatus 100 includes a control unit 20, a medium conveyance mechanism 22, a movement 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 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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 3 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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. As will be described later, as shown in Figure 6, the upper electrode 52 has a first hydrogen absorption layer 524 and a second hydrogen absorption layer 522. Furthermore, as shown in Figure 6, the piezoelectric element 5 further has a third hydrogen absorption layer 54 and a fourth hydrogen absorption layer 55. Note that the piezoelectric layer 53, the third hydrogen absorption layer 54, and the fourth 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.

[0036] 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.

[0037] 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 made of a perovskite-type composite oxide.

[0038] 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.

[0039] A voltage equivalent to the difference between the reference voltage applied to the upper electrode 52 and the drive voltage 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.

[0040] 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.

[0041] 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).

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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 third hydrogen absorption layer 54, and a fourth hydrogen absorption layer 55. The lower electrode 51, the piezoelectric layer 53, and the upper electrode 52 are each composed of multiple layers. In this embodiment, the third hydrogen absorption layer 54 is placed between the lower electrode 51 and the piezoelectric layer 53. The fourth hydrogen absorption layer 55 is placed between the multiple layers that make up the piezoelectric layer 53. Therefore, the fourth hydrogen absorption layer 55 is located inside the piezoelectric layer 53.

[0046] 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.

[0047] The second electrode layer 512 is positioned between the first electrode layer 511 and the third 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.

[0048] 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.

[0049] The third hydrogen absorption layer 54 has the function of absorbing hydrogen present in each layer or between layers that constitute the piezoelectric element 5. In particular, the third hydrogen absorption layer 54 suitably absorbs hydrogen in the piezoelectric layer 53, hydrogen in the lower electrode 51, and hydrogen present at the interfaces of each layer below the piezoelectric layer 53.

[0050] In Figure 6, the interface between the third 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 third hydrogen absorption layer 54 may be embedded in, dispersed in, or integrated with the piezoelectric layer 53. Also, the composition within the third hydrogen absorption layer 54 may be constant or graded. Therefore, the composition of the third hydrogen absorption layer 54 may differ between the piezoelectric layer 53 side and the lower electrode 51 side. Furthermore, the thickness of the third 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 third hydrogen absorption layer 54 may be composed of multiple layers.

[0051] 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.

[0052] Each layer constituting the piezoelectric layer 53 is made of a perovskite-type composite oxide. More specifically, each layer includes, for example, lead titanate (PbTiO3), lead zirconate titanate (PZT:Pb(Zr,Ti)O3), lead zirconate (PbZrO3), lead lanthanum titanate ((Pb,La),TiO3), lead lanthanum zirconate titanate ((Pb,La)(Zr,Ti)O3), lead zirconium niobate titanate (Pb(Zr,Ti,Nb)O3), lead zirconium magnesium niobate titanate (Pb(Zr,Ti)(Mg,Nb)O3), etc. Note that each layer constituting the piezoelectric layer 53 may be made of a lead-free material. Examples of lead-free materials include bismuth ironate (BiFeO3), barium titanate (BaTiO3), and potassium sodium niobate ((K,Na)(NbO3)).

[0053] 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.

[0054] The first layer 531 is positioned between the third hydrogen absorption layer 54 and the fourth hydrogen absorption layer 55 and is in contact with them. The fourth hydrogen absorption layer 55 is positioned between the first layer 531 and the second layer 532 and is in contact with them.

[0055] The fourth 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 fourth hydrogen absorption layer 55 preferably absorbs hydrogen in the first layer 531 and the second layer 532.

[0056] In Figure 6, the interface between the fourth hydrogen absorption layer 55 and the second layer 532, and the interface between the fourth 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 fourth 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 fourth hydrogen absorption layer 55 may be constant or gradient. Therefore, the composition of the fourth hydrogen absorption layer 55 may differ on the second layer 532 side and the first layer 531 side. Furthermore, the thickness of the fourth 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 D5 of the fourth hydrogen absorption layer 55 is thinner than the film thickness D4 of the third hydrogen absorption layer 54, but it may be greater than or equal to the film thickness D4 of the third hydrogen absorption layer 54. Furthermore, the fourth hydrogen absorption layer 55 may be composed of multiple layers.

[0057] The upper electrode 52 is a structure in which a third electrode layer 521, a second hydrogen absorption layer 522, an electrode layer 523, and a first 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.

[0058] The second hydrogen absorption layer 522 is, for example, titanium oxide (TiO x ) is included. The film thickness D2 of the second hydrogen absorption layer 522 along the Z axis is not particularly limited, but for example, it is 2 nm or more and 20 nm or less. The second hydrogen absorption layer 522 has the function of absorbing hydrogen present in the upper electrode 52, hydrogen present in the piezoelectric element 5, and hydrogen entering from outside the piezoelectric element 5. The composition of the second hydrogen absorption layer 522 may be constant or gradient within the layer. Furthermore, the second hydrogen absorption layer 522 may be formed of multiple layers.

[0059] The electrode layer 523 contains, for example, iridium (Ir). The thickness of the electrode layer 523 along the Z axis is not particularly limited, but is, for example, 5 nm or more and 50 nm or less.

[0060] The first hydrogen absorption layer 524 contains, for example, titanium (Ti). The film thickness D1 of the first hydrogen absorption layer 524 along the Z axis is not particularly limited, but is, for example, 5 nm to 30 nm. The first hydrogen absorption layer 524 has the function of absorbing hydrogen present in the upper electrode 52, hydrogen present in the piezoelectric element 5, and hydrogen entering from outside the piezoelectric element 5. The composition of the first hydrogen absorption layer 524 may be constant or gradient within the layer. Furthermore, the first hydrogen absorption layer 524 may be formed from multiple layers.

[0061] 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 third hydrogen absorption layer 54 and the piezoelectric layer 53, but such an orientation control layer may be provided. Furthermore, the third hydrogen absorption layer 54 may also have the function of such an orientation control layer. Because the third 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.

[0062] Similarly, although an orientation control layer for controlling the orientation of the second layer 532 is not provided between the fourth hydrogen absorption layer 55 and the second layer 532, such an orientation control layer may be provided. The fourth hydrogen absorption layer 55 may have the function of such an orientation control layer. However, since the fourth 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.

[0063] 1-4. Hydrogen absorption layer As described above, the upper electrode 52 has a first hydrogen absorption layer 524. The piezoelectric element 5 having the first hydrogen absorption layer 524 can absorb hydrogen outside the piezoelectric element 5, hydrogen present at the interface between the upper electrode 52 and other layers, hydrogen present in the piezoelectric layer 53, or hydrogen that may enter the piezoelectric layer 53.

[0064] The hysteresis characteristics of the piezoelectric element 5 change significantly depending on the hydrogen content of the piezoelectric layer 53 compared to the design stage. When the hysteresis characteristics change significantly, there is a risk that the difference in displacement between multiple piezoelectric elements 5 will become large. Therefore, in order to reduce the difference in displacement between multiple piezoelectric elements 5, it is necessary to change the drive voltage and waveform for each piezoelectric element 5. Adjusting the difference in displacement between multiple piezoelectric elements 5 in this way is time-consuming and inconvenient.

[0065] Furthermore, when the piezoelectric element 5 has a piezoelectric layer 53 formed from multiple layers, the hydrogen content of the piezoelectric layer 53 tends to be higher than that at the design stage. 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. Moreover, not only when the composition in the piezoelectric layer 53 is constant, but also when there is a compositional gradient in the piezoelectric layer 53, differences in displacement occur among multiple piezoelectric elements 5 due to the hydrogen content of the piezoelectric layer 53.

[0066] As described above, the piezoelectric element 5 of this embodiment has a first hydrogen absorption layer 524 on its upper electrode 52. Therefore, during the manufacturing and use of the piezoelectric element 5, it can absorb hydrogen present in the piezoelectric layer 53, or hydrogen that may enter the piezoelectric layer 53. This suppresses a large change in the hysteresis characteristics of the piezoelectric element 5 compared to the design stage due to the hydrogen content of the piezoelectric layer 53. Consequently, it suppresses a large difference in displacement due to changes in the hysteresis characteristics of multiple piezoelectric elements 5. Therefore, it eliminates the need to change the drive voltage and waveform for each piezoelectric element 5, thus suppressing a deterioration in usability. For this reason, the liquid discharge head 3 equipped with such piezoelectric elements 5 has excellent displacement characteristics and usability.

[0067] Furthermore, in this embodiment, as shown in Figure 4, the upper electrode 52 is a common electrode located above the piezoelectric layer 53 and provided to cover the piezoelectric layer 53. Therefore, compared to the case where the upper electrode 52 is an individual electrode that does not cover the piezoelectric layer 53, it is possible to suppress hydrogen from entering the piezoelectric layer 53 from outside the piezoelectric element 5. In particular, even after manufacturing, it is possible to effectively suppress hydrogen from entering the piezoelectric layer 53 from outside the piezoelectric element 5.

[0068] The first hydrogen absorption layer 524 is composed of a material capable of absorbing hydrogen. Specifically, the first hydrogen absorption layer 524 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 524 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 524 is composed of, for example, titanium or lead titanate (PbTiO3). Alternatively, the first hydrogen absorption layer 524 may be composed of, for example, a composite oxide containing bismuth (Bi), iron (Fe), titanium (Ti), and lead (Pb).

[0069] Furthermore, the second hydrogen absorption layer 522, the third hydrogen absorption layer 54, and the fourth hydrogen absorption layer 55 each similarly contain a hydrogen storage material that can combine with hydrogen to form a hydride.

[0070] Furthermore, the film thickness D1 of the first hydrogen absorption layer 524 is not particularly limited, but is preferably 10 nm to 25 nm. When the film thickness D1 of the first hydrogen absorption layer 524 is within the above range, it is possible to absorb hydrogen while suppressing the diffusion of hydrogen from the first hydrogen absorption layer 524 due to deterioration over time, compared to when it is outside the range. Thus, it is possible to provide a piezoelectric element with stable and excellent displacement characteristics.

[0071] Furthermore, as mentioned above, the upper electrode 52 has a second hydrogen absorption layer 522 that is different from the first hydrogen absorption layer 524. By having the second hydrogen absorption layer 522 in addition to the first hydrogen absorption layer 524, the penetration of hydrogen into the piezoelectric layer 53 can be suppressed more effectively.

[0072] In this embodiment, the second hydrogen absorption layer 522 is located below the first hydrogen absorption layer 524. Therefore, the second hydrogen absorption layer 522 is positioned closer to the piezoelectric layer 53 than the first hydrogen absorption layer 524. By providing the second hydrogen absorption layer 522 near the piezoelectric layer 53, hydrogen can be suitably absorbed between the interface between the piezoelectric layer 53 and the upper electrode 52.

[0073] The second hydrogen absorption layer 522 may be provided above the first hydrogen absorption layer 524. In this embodiment, the second hydrogen absorption layer 522 is spaced apart from the first hydrogen absorption layer 524, but may be in contact with the first hydrogen absorption layer 524. The first hydrogen absorption layer 524 and the second hydrogen absorption layer 522 may be made of the same material or of different materials.

[0074] Furthermore, in the direction along the Z-axis, which is the stacking direction, the film thickness D1 of the first hydrogen absorption layer 524 is preferably thicker than the film thickness D2 of the second hydrogen absorption layer 522. In this embodiment, the first hydrogen absorption layer 524 is closer to the outside than the second hydrogen absorption layer 522. By increasing the film thickness D1 of the first hydrogen absorption layer 524, the penetration of hydrogen into the piezoelectric layer 53 can be suppressed more effectively. Also, by making the film thickness D2 of the second hydrogen absorption layer 522 thinner, the amount of hydrogen absorbed by the second hydrogen absorption layer 522 can be reduced. Even if hydrogen is released from the second hydrogen absorption layer 522 due to changes over time, the amount of hydrogen that penetrates the piezoelectric layer 53 can be reduced.

[0075] Note that film thickness D1 may be less than or equal to film thickness D2.

[0076] Figure 7 shows the measurement results of a secondary ion mass spectrometer (SIMS) for the piezoelectric element 5 of this embodiment. In Figure 7, the material of the first electrode layer 511 is platinum, and the material of the second electrode layer 512 is iridium. The third hydrogen absorption layer 54 contains titanium. The material of each layer of the piezoelectric layer 53 is lead zirconate titanate (PZT). The fourth hydrogen absorption layer 55 contains titanium. The material of the third electrode layer 521 is iridium oxide, and the material of the electrode layer 523 is iridium. The material of the second hydrogen absorption layer 522 is titanium oxide, and the material of the first hydrogen absorption layer 524 is titanium.

[0077] The horizontal axis in Figure 7 represents depth [nm]. Since the analysis was performed in the Z1 direction from the upper electrode 52, the shallower depths are on the upper electrode 52 side, and the deeper depths are on the lower electrode 51 side.

[0078] The vertical axis of Figure 7 shows the hydrogen concentration [atoms / cc]. This hydrogen concentration was determined using standard samples doped with the target element at known concentrations. Titanium and zirconium are shown in terms of ionic intensity. While Figure 7 shows clear line segments along the interfaces of each layer, the exact location of the interfaces may vary slightly depending on the interpretation.

[0079] As can be seen from Figure 7, the hydrogen content of the first hydrogen absorption layer 524 is greater than that of the second hydrogen absorption layer 522. Therefore, it is considered that the first hydrogen absorption layer 524 is able to more effectively suppress the intrusion of hydrogen from outside the piezoelectric element 5 into the piezoelectric layer 53. In addition, because the hydrogen content of the second hydrogen absorption layer 522 is low, even if hydrogen is released from the second hydrogen absorption layer 522 due to changes over time, etc., it is possible to suppress the intrusion of hydrogen into the piezoelectric layer 53.

[0080] Furthermore, the hydrogen content of the first hydrogen absorption layer 524 may be less than or equal to the hydrogen content of the second hydrogen absorption layer 522.

[0081] Furthermore, as described above, the upper electrode 52 has an electrode layer 523 made of a conductive material. In this embodiment, the electrode layer 523 is provided between the second hydrogen absorption layer 522 and the first hydrogen absorption layer 524 in the direction along the Z-axis, which is the stacking direction. Therefore, the second hydrogen absorption layer 522 and the first hydrogen absorption layer 524 are sandwiched between the electrode layer 523.

[0082] When the electrode layer 523 is deposited by, for example, sputtering, a large amount of hydrogen may be present on the surface of the electrode layer 523. In this case, by providing a second hydrogen absorption layer 522 and a first hydrogen absorption layer 524 so as to sandwich the electrode layer 523, the hydrogen on the surface of the electrode layer 523 can be suitably absorbed by the second hydrogen absorption layer 522 and the first hydrogen absorption layer 524. Therefore, the penetration of the hydrogen into the piezoelectric layer 53 can be effectively suppressed.

[0083] The electrode layer 523 may be provided at a location other than between the second hydrogen absorption layer 522 and the first hydrogen absorption layer 524.

[0084] As can also be seen from Figure 7, the hydrogen content of the electrode layer 523 is lower than that of the first hydrogen absorption layer 524. Furthermore, the hydrogen content of the electrode layer 523 is lower than that of the second hydrogen absorption layer 522. By providing the first hydrogen absorption layer 524 and the second hydrogen absorption layer 522, the hydrogen content in the electrode layer 523 can be reduced. Therefore, the risk of increased electrical resistance due to deficiency or deterioration of crystallinity in the electrode layer 523 can be suppressed. In addition, the low hydrogen content of the electrode layer 523 can suppress an increase in electrical resistance.

[0085] Furthermore, a third electrode layer 521, different from the electrode layer 523, is provided between the second hydrogen absorption layer 522 and the piezoelectric layer 53. As can be seen from Figure 7, the hydrogen content of the third electrode layer 521 is lower than that of the first hydrogen absorption layer 524 and the second hydrogen absorption layer 522. Therefore, the risk of increased electrical resistance due to deficiency or deterioration of crystallinity in the third electrode layer 521 can be suppressed. In addition, the low hydrogen content of the third electrode layer 521 can suppress an increase in electrical resistance. Furthermore, the low hydrogen content of the third electrode layer 521 can reduce the intrusion of hydrogen from the upper electrode 52 into the piezoelectric layer 53.

[0086] As described above, the piezoelectric element 5 has a third hydrogen absorption layer 54. In this embodiment, the third hydrogen absorption layer 54 is positioned between the piezoelectric layer 53 and the lower electrode 51. The third hydrogen absorption layer 54 has the function of absorbing hydrogen. By providing the third hydrogen absorption layer 54 on the lower electrode 51 side relative to the piezoelectric layer 53, the intrusion of hydrogen from the lower electrode 51 side into the piezoelectric layer 53 can be suppressed compared to the case where the third hydrogen absorption layer 54 is not provided.

[0087] The third hydrogen absorption layer 54 may be omitted.

[0088] Furthermore, the piezoelectric element 5 has a fourth hydrogen absorption layer 55. In this embodiment, the fourth hydrogen absorption layer 55 is located within the piezoelectric layer 53. Specifically, it is provided between the first layer 531 and the second layer 532. By providing such a fourth hydrogen absorption layer 55, the hydrogen content of the piezoelectric layer 53 can be reduced compared to when it is not provided.

[0089] The fourth hydrogen absorption layer 55 may be omitted.

[0090] As can be seen from Figure 7, the hydrogen content of the first layer 531 is lower than that of the second layer 532. The first layer 531 is stacked above the third hydrogen absorption layer 54 and is in direct contact with the third hydrogen absorption layer 54. The second layer 532 is stacked above the first layer 531. Furthermore, the first layer 531 is positioned between the third hydrogen absorption layer 54 and the fourth hydrogen absorption layer 55 and is in contact with them. Therefore, the functions of the third hydrogen absorption layer 54 and the fourth hydrogen absorption layer 55 make it possible to reduce the hydrogen content of the first layer 531 to that of the second layer 532. Note that the hydrogen content of the first layer 531 may be higher than or equal to that of the second layer 532.

[0091] Furthermore, as can be seen from Figure 7, the hydrogen content of the third hydrogen absorption layer 54 is greater than that of the first layer 531. The third hydrogen absorption layer 54 absorbs hydrogen, thereby reducing the hydrogen content of the first layer 531. The presence of this third hydrogen absorption layer 54 suppresses the intrusion of hydrogen into the piezoelectric layer 53, including the first layer 531, both after the manufacture of the piezoelectric element 5 and during use. In addition, the third hydrogen absorption layer 54 suppresses the increase in the hydrogen content of the first layer 531 during manufacture, thereby suppressing the increase in the hydrogen content of the second layer 532 to the sixth layer 536 on the first layer 531.

[0092] Furthermore, as shown in Figure 6, the third hydrogen absorption layer 54 is provided on the lower electrode 51. Preferably, the third hydrogen absorption layer 54 is also provided on the portion of the diaphragm 33 shown in Figure 4 where the lower electrode 51 is not provided above, in addition to above the lower electrode 51. With the third hydrogen absorption layer 54 provided in this way, the entire lower surface of the first layer 531 is in contact with the third hydrogen absorption layer 54. Therefore, compared to a configuration where only a part of the lower surface of the first layer 531 is in contact with the third hydrogen absorption layer 54, the function of the third hydrogen absorption layer 54 can suppress the increase in the hydrogen content of the first layer 531. Note that the hydrogen content of the third hydrogen absorption layer 54 may be less than or equal to the hydrogen content of the first layer 531.

[0093] Furthermore, the hydrogen content of the second layer 532 of the piezoelectric layer 53 is lower than that of the third layer 533. The second layer 532 is stacked above the fourth hydrogen absorption layer 55 and is in contact with the fourth hydrogen absorption layer 55. The third layer 533 is stacked above the second layer 532. Therefore, the second layer 532 is positioned closer to the fourth hydrogen absorption layer 55 than the third layer 533. Consequently, the hydrogen absorption function of the fourth hydrogen absorption layer 55 allows for a lower hydrogen content in the second layer 532.

[0094] Furthermore, as can be seen from Figure 7, the hydrogen content of the fourth hydrogen absorption layer 55 is lower than that of the third hydrogen absorption layer 54. It is thought that the third hydrogen absorption layer 54 and the fourth hydrogen absorption layer 55 mainly suppress the intrusion of hydrogen from the lower electrode 51 side into the piezoelectric layer 53. It is thought that the third hydrogen absorption layer 54 alone can sufficiently absorb hydrogen from the lower electrode 51 side. For this reason, it is thought that the hydrogen content of the fourth hydrogen absorption layer 55 is lower than that of the third hydrogen absorption layer 54. However, the hydrogen content of the fourth hydrogen absorption layer 55 may be higher than or equal to that of the third hydrogen absorption layer 54.

[0095] In this embodiment, the film thickness D5 of the fourth hydrogen absorption layer 55 is thinner than the film thickness D4 of the third hydrogen absorption layer 54 in the direction along the Z axis. Therefore, film thickness D4 is thicker than film thickness D5. Because film thickness D4 is thicker than film thickness D5, the penetration of hydrogen from the lower electrode 51 side into the piezoelectric layer 53 by the third hydrogen absorption layer 54 can be suppressed compared to the case where it is thinner. Note that the film thickness D5 of the fourth hydrogen absorption layer 55 may be greater than or equal to the film thickness D4 of the third hydrogen absorption layer 54.

[0096] As shown in Figure 7, the variation in the average value of the hydrogen content in the central part of the piezoelectric element 5 in the stacking direction is preferably 24% or less. The central part is the layer located in the center of the piezoelectric layer 53 in the stacking direction and is not in contact with any layers other than the piezoelectric layer 53. In the example of Figure 6, the central part is the third layer 533 and the fourth layer 534. These layers are not in contact with the fourth hydrogen absorption layer 55 and the upper electrode 52, which are layers other than the piezoelectric layer 53.

[0097] In the example shown in Figure 7, the variation is 24% or less. By keeping the variation below 24%, it is possible to suppress the steepness of the slope of the hysteresis curve, which shows the relationship between the voltage and polarization of the piezoelectric layer 53, compared to the case where the variation exceeds 24%. Furthermore, it is possible to suppress changes in the shape of the hysteresis curve over time from the design stage. Therefore, a decrease in the displacement characteristics of the piezoelectric element 5 can be suppressed. Note that the variation relative to the average value of the hydrogen content in the central region may exceed 24%.

[0098] Furthermore, as shown in Figure 7, the hydrogen content of the third layer 533 and the fourth layer 534, which are the central parts of the piezoelectric layer 53, is suppressed in the same way as the hydrogen content of the first layer 531. Specifically, for example, the average hydrogen content of each layer in the central part of the piezoelectric layer 53 is preferably less than 1E+20 [atoms / cc], and more preferably less than 1E+19 [atoms / cc]. 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 19This represents the performance of the piezoelectric element 5, where the displacement of the piezoelectric layer 53 away from the neutral axis A1, as shown in Figure 4, is greater. The third layer 533 and the fourth layer 534 are further away from the neutral axis A1 than the first layer 531. By reducing the hydrogen content of the third layer 533 and the fourth layer 534, which are further away from the neutral axis A1, the deterioration of the displacement characteristics of the piezoelectric element 5 can be suppressed.

[0099] Furthermore, as mentioned above, the piezoelectric layer 53 is composed of a perovskite-type composite oxide, and is preferably composed of lead zirconate titanate (PZT). The use of PZT in the piezoelectric layer is particularly effective in suppressing changes in the hysteresis characteristics of the piezoelectric element 5 caused by the provision of the third hydrogen absorption layer 54. Moreover, when the piezoelectric layer 53 is composed of multiple layers, the effects of providing the third hydrogen absorption layer 54 can be particularly pronounced.

[0100] Furthermore, it is particularly preferable that each of the first hydrogen absorption layer 524, the second hydrogen absorption layer 522, the third hydrogen absorption layer 54, and the fourth hydrogen absorption layer 55 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.

[0101] 1-5. Manufacturing method of piezoelectric element 5 Figure 8 shows the flow of the manufacturing method for the piezoelectric element 5 shown in Figure 6. As shown in Figure 8, 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.

[0102] 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.

[0103] The intermediate layer formation step S12 includes the formation of a third hydrogen absorption layer 54, a piezoelectric layer 53, and a second hydrogen absorption layer. 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. Then, the layer containing the hydrogen storage material and the first layer precursor are fired. As a result, the third hydrogen absorption layer 54 and the first layer 531 are formed.

[0104] 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. Next, the other layer containing the hydrogen storage material and the second layer precursor are fired. As a result, the fourth hydrogen absorption layer 55 and the second layer 532 are formed.

[0105] When forming the fourth hydrogen absorption layer 55, there is a risk that moisture may remain on the surface of the first layer 531 when the fourth hydrogen absorption layer 55 is formed. For this reason, it is preferable to perform a heating step to remove surface moisture when forming the fourth 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 fourth hydrogen absorption layer 55 is reduced when it is formed, so that the fourth hydrogen absorption layer 55 can absorb hydrogen sufficiently after formation.

[0106] 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 third hydrogen absorption layer 54, the fourth hydrogen absorption layer 55, and the piezoelectric layer 53 are calcined together.

[0107] When each layer of the piezoelectric layer 53 is formed using a sol-gel, 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, when the third layer 533 is formed using a sol-gel.

[0108] 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 second hydrogen absorption layer 522, an electrode layer 523, and a first 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 second hydrogen absorption layer 522 containing a metal oxide is formed on the third electrode layer 521 by sputtering, vapor deposition, or CVD, followed by firing.

[0109] Next, an electrode layer 523 is formed on the second hydrogen absorption layer 522 by depositing a layer containing a conductive material such as iridium using sputtering, vapor deposition, or CVD. Then, a first hydrogen absorption layer 524 is formed on the 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.

[0110] When forming the first hydrogen absorption layer 524, there is a risk that moisture may remain on the surface of the electrode layer 523 during the formation of the first hydrogen absorption layer 524. For this reason, it is preferable to perform a heating step to remove surface moisture during the formation of the first hydrogen absorption layer 524. This reduces the amount of moisture remaining on the surface of the electrode layer 523. As a result, the first hydrogen absorption layer 524 can absorb hydrogen sufficiently after formation.

[0111] 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.

[0112] 2-1. First variation Figure 9 is a schematic diagram of the piezoelectric element 5A of the first modified example. As shown in Figure 9, the third hydrogen absorption layer 54A of the piezoelectric element 5A of the first modified example consists of multiple layers with different constituent elements. Specifically, the third hydrogen absorption layer 54A includes a first absorption layer 541 and a second absorption layer 542. 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.

[0113] Since the third 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.

[0114] 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.

[0115] In the first embodiment and the first modified example, a portion of the lower electrode 51 may be considered as part of the third hydrogen absorption layer 54, and in this case as well, the third 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 third hydrogen absorption layer 54. Furthermore, the third hydrogen absorption layer 54 may also function as an electrode.

[0116] 2-2. Second variation Figure 10 is a schematic diagram showing the piezoelectric element 5B of the second modified example. As shown in Figure 10, the third hydrogen absorption layer 54B of the second modified example is provided below the lower electrode 51 in the direction along the Z-axis, which is the stacking direction. The third hydrogen absorption layer 54B is positioned between the diaphragm 33 and the lower electrode 51 and is in contact with them.

[0117] By positioning the third hydrogen absorption layer 54B below the lower electrode 51, it is possible to suppress the intrusion of hydrogen into the piezoelectric layer 53 from the diaphragm 33 side.

[0118] 2-3. Third Variation Figure 11 is a cross-sectional view of the piezoelectric element 5 of the third modified example. As shown in Figure 11, 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.

[0119] 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, a third electrode layer 521, a second hydrogen absorption layer 522, and an electrode layer 523 are arranged below the protective film 6. A first hydrogen absorption layer 524 is arranged above the protective film 6. A portion of the first hydrogen absorption layer 524 is provided on the first hydrogen absorption layer 524, so that the first 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.

[0120] The first hydrogen absorption layer 524 may be located below the protective film 6. Furthermore, while the first 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.

[0121] 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 second hydrogen absorption layer 522, and the electrode layer 523, and the formation of the first 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 second hydrogen absorption layer 522, and the electrode layer 523 are not provided. The protective film 6 is formed by depositing a ceramic material using sputtering, vapor deposition, or CVD.

[0122] Figure 12 shows the measurement results of a secondary ion mass spectrometer for the piezoelectric element of the third modified example. As can be seen from Figure 12, in this modified example, as in the first embodiment, the hydrogen content of the first hydrogen absorption layer 524 is greater than the hydrogen content of the second hydrogen absorption layer 522. The hydrogen content of the electrode layer 523 is less than the hydrogen content of the first hydrogen absorption layer 524 and the second hydrogen absorption layer 522. The hydrogen content of the third electrode layer 521 is less than the hydrogen content of the first hydrogen absorption layer 524 and the second hydrogen absorption layer 522. The hydrogen content of the first layer 531 is less than the hydrogen content of the second layer 532. Furthermore, the hydrogen content of the third hydrogen absorption layer 54 is greater than the hydrogen content of the first layer 531. Furthermore, the hydrogen content of the fourth hydrogen absorption layer 55 is less than the hydrogen content of the third hydrogen absorption layer 54.

[0123] Furthermore, in the example shown in Figure 12, the variation in the average value of the hydrogen content at the central part in the stacking direction of the piezoelectric element 5 is preferably 24% or less.

[0124] 2-4. Fourth Variation Figure 13 is a schematic diagram of the piezoelectric element 5C of the fourth modified example. As shown in Figure 13, the piezoelectric element 5C of the fourth modified example has a hydrogen barrier layer 56 at the top layer in the stacking direction that suppresses the intrusion of hydrogen. The hydrogen barrier layer 56 includes, for example, ceramics such as aluminum oxide (AlOx) and silicon nitride. By providing the hydrogen barrier layer 56, it is possible to suppress the intrusion of external hydrogen into the piezoelectric layer 53 compared to when it is not provided.

[0125] 2-5. Other variations The "liquid dispensing head" may be a circulating type head having a so-called circulation channel.

[0126] "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.

[0127] 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.

[0128] 3. Addendum From the above embodiments or modifications, for example, the following embodiments can be understood.

[0129] A piezoelectric element according to a first embodiment, which is a preferred example of the present disclosure, is a piezoelectric element in which a lower electrode, a piezoelectric layer made of a perovskite-type composite oxide, and an upper electrode are stacked in the stacking direction, wherein the upper electrode has a first hydrogen absorption layer that absorbs hydrogen.

[0130] According to this first embodiment, hydrogen present at the interface between the upper electrode and other layers, hydrogen present in the piezoelectric layer, or hydrogen that may enter the piezoelectric layer can be absorbed. Therefore, changes in hysteresis characteristics due to an increase in the hydrogen content in the piezoelectric layer can be suppressed. Consequently, the risk of differences in displacement between piezoelectric elements can be suppressed. Therefore, it is not necessary to adjust for such differences by changing the driving voltage or waveform for each piezoelectric element, thereby improving ease of use.

[0131] In the piezoelectric element of the second embodiment, which is a preferred example of the first embodiment, the upper electrode has a second hydrogen absorption layer different from the first hydrogen absorption layer.

[0132] According to this second embodiment, the penetration of hydrogen into the piezoelectric layer can be suppressed more effectively.

[0133] In the piezoelectric element of the third embodiment, which is a preferred example of the second embodiment, the thickness of the first hydrogen absorption layer is greater than the thickness of the second hydrogen absorption layer in the stacking direction.

[0134] According to this third embodiment, the penetration of hydrogen can be more effectively suppressed by increasing the thickness of the first hydrogen absorption layer, which is closer to the outside. Furthermore, by making the thickness of the second hydrogen absorption layer thinner, the amount of hydrogen absorbed by the second hydrogen absorption layer is reduced, and even if hydrogen is released from the second hydrogen absorption layer due to changes over time, etc., the penetration of hydrogen into the piezoelectric layer can be suppressed.

[0135] In the piezoelectric element of the fourth embodiment, which is a preferred example of the second or third embodiment, the hydrogen content of the first hydrogen absorption layer is greater than the hydrogen content of the second hydrogen absorption layer.

[0136] According to this fourth embodiment, the intrusion of hydrogen can be suppressed more effectively.

[0137] In a piezoelectric element of the fifth embodiment, which is a preferred example of any of the second to fourth embodiments, the upper electrode has an electrode layer made of a conductive material, and the electrode layer is provided between the second hydrogen absorption layer and the first hydrogen absorption layer in the stacking direction.

[0138] When the electrode layer is deposited by, for example, sputtering, a large amount of hydrogen may be present on the surface of the electrode layer. In this case, by providing a second hydrogen absorption layer and a first hydrogen absorption layer sandwiching the electrode layer, the hydrogen on the surface of the electrode layer can be absorbed. Therefore, the penetration of the hydrogen into the piezoelectric layer can be suppressed.

[0139] In a piezoelectric element of the sixth embodiment, which is a preferred example of any of the second to fifth embodiments, the upper electrode has an electrode layer made of a conductive material, and the hydrogen content of the electrode layer is smaller than the hydrogen content of the first hydrogen absorption layer.

[0140] According to this sixth embodiment, the provision of a first hydrogen absorption layer and a second hydrogen absorption layer reduces the hydrogen content in the electrode layer. This suppresses the risk of increased electrical resistance due to deficiency or deterioration of crystallinity in the electrode layer. Furthermore, the low hydrogen content in the electrode layer suppresses the increase in electrical resistance.

[0141] In the piezoelectric element of the seventh embodiment, which is a preferred example of the sixth embodiment, the thickness of the first hydrogen absorption layer is 10 nm or more and 25 nm or less.

[0142] By having a film thickness of the first hydrogen absorption layer within the above range, it is possible to absorb hydrogen while suppressing the diffusion of hydrogen from the first hydrogen absorption layer due to deterioration over time, compared to when it is outside the range. Therefore, it is possible to provide a piezoelectric element with stable and excellent displacement characteristics.

[0143] In the piezoelectric element of the eighth embodiment, which is a preferred example of any of the first to seventh embodiments, the piezoelectric layer consists of multiple layers, and the variation in the average value of the hydrogen content in the central part of the piezoelectric layer is 24% or less.

[0144] By keeping this variation below 24%, it is possible to suppress changes in the shape of the hysteresis curve, which shows the relationship between the voltage and polarization of the piezoelectric material, from the time of design, compared to cases where the variation exceeds 24%.

[0145] In a piezoelectric element of the ninth embodiment, which is a preferred example of any of the first to eighth embodiments, a protective film is provided on the piezoelectric layer and protects the piezoelectric layer, and the first hydrogen absorption layer is provided on the protective film.

[0146] By providing a protective film, it is possible to suppress hydrogen from entering the piezoelectric layer. Furthermore, since a first hydrogen absorption layer is provided on the protective film, it can absorb hydrogen in the protective film, thereby suppressing hydrogen from entering the piezoelectric layer.

[0147] In the piezoelectric element of the tenth embodiment, which is a preferred example of any of the first to ninth embodiments, a third hydrogen absorption layer that absorbs hydrogen is provided between the piezoelectric layer and the lower electrode, or on the lower electrode.

[0148] By providing a third hydrogen absorption layer on the lower electrode side, the intrusion of hydrogen from the lower electrode side into the piezoelectric layer can be suppressed.

[0149] In the piezoelectric element of the 11th embodiment, which is a preferred example of any of the first to tenth embodiments, the piezoelectric layer is made of lead zirconate titanate.

[0150] When the piezoelectric layer is made of lead titanate, the first hydrogen absorption layer can be used to suppress changes in the hysteresis characteristics of the piezoelectric element 5.

[0151] In the piezoelectric element according to the 12th embodiment, which is a preferred example of any of the 1st to 11th embodiments, the uppermost layer in the stacking direction has a hydrogen barrier layer that suppresses the intrusion of hydrogen.

[0152] The presence of such a hydrogen barrier layer can suppress the intrusion of hydrogen from outside the piezoelectric element into the piezoelectric layer.

[0153] 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 eleventh embodiments.

[0154] This allows us to provide a liquid dispensing head with excellent displacement characteristics and ease of use. [Explanation of Symbols]

[0155] 3...Liquid discharge head, 5...Piezoelectric element, 6...Protective film, 51...Lower electrode, 52...Upper electrode, 53...Piezoelectric layer, 54...Third hydrogen absorption layer, 55...Fourth hydrogen absorption layer, 56...Hydrogen barrier layer, 331...First vibrator layer, 332...Second vibrator layer, 511...First electrode layer, 512...Second electrode layer, 521...Third electrode layer, 522...Second hydrogen absorption layer, 523...Electrode layer, 524...First hydrogen absorption layer, 531...First layer, 532...Second layer, 533...Third layer, 534...Fourth layer, 535...Fixed layer, 536...Sixth layer, 541...First absorption layer, 542...Second absorption layer, A1...Neutral axis, C1...Pressure chamber, D1...Film thickness, D2...Film thickness, D4...Film thickness, D5...Film thickness, N...Nozzle.

Claims

1. A piezoelectric element comprising a lower electrode, a piezoelectric layer made of a perovskite-type composite oxide, and an upper electrode, stacked in the stacking direction, The upper electrode has a first hydrogen absorption layer that absorbs hydrogen. A piezoelectric element characterized by the following features.

2. In the piezoelectric element according to claim 1, The upper electrode has a second hydrogen absorption layer that is different from the first hydrogen absorption layer. A piezoelectric element characterized by the following features.

3. In the piezoelectric element according to claim 2, In the aforementioned stacking direction, the thickness of the first hydrogen absorption layer is greater than the thickness of the second hydrogen absorption layer. A piezoelectric element characterized by the following features.

4. In the piezoelectric element according to claim 2, The hydrogen content of the first hydrogen absorption layer is greater than the hydrogen content of the second hydrogen absorption layer. A piezoelectric element characterized by the following features.

5. In the piezoelectric element according to claim 2, The upper electrode has an electrode layer made of a conductive material, The electrode layer is provided between the second hydrogen absorption layer and the first hydrogen absorption layer in the stacking direction. A piezoelectric element characterized by the following features.

6. In the piezoelectric element according to claim 2, The upper electrode has an electrode layer made of a conductive material, The hydrogen content of the electrode layer is smaller than the hydrogen content of the first hydrogen absorption layer. A piezoelectric element characterized by the following features.

7. In a piezoelectric element according to any one of claims 1 to 6, The thickness of the first hydrogen absorption layer is 10 nm or more and 25 nm or less. A piezoelectric element characterized by the following features.

8. In a piezoelectric element according to any one of claims 1 to 6, The piezoelectric layer consists of multiple layers. The variation in the average value of the hydrogen content in the central part of the piezoelectric layer is 24% or less. A piezoelectric element characterized by the following features.

9. In a piezoelectric element according to any one of claims 1 to 6, A protective film is provided on the piezoelectric layer and protects the piezoelectric layer, The first hydrogen absorption layer is provided on the protective film. A piezoelectric element characterized by the following features.

10. In a piezoelectric element according to any one of claims 1 to 6, Between the piezoelectric layer and the lower electrode, or on the lower electrode, there is a third hydrogen absorption layer that absorbs hydrogen. A piezoelectric element characterized by the following features.

11. In a piezoelectric element according to any one of claims 1 to 6, The uppermost layer in the stacking direction has a hydrogen barrier layer that suppresses the intrusion of hydrogen. A piezoelectric element characterized by the following features.

12. A piezoelectric element according to any one of claims 1 to 6, A liquid dispensing head characterized by the following features.

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