piezoelectric element

Abstract

A piezoelectric element that suppresses generation of a crack in a piezoelectric layer. The piezoelectric element (44) includes: a close contact layer (445) formed on a vibrating plate (36) and containing titanium; a lower electrode (441) formed on the close contact layer (445); a diffusion suppression layer (447) formed on the lower electrode (441) and containing iridium; a seed layer (442) formed on the diffusion suppression layer (447) and containing bismuth; a piezoelectric layer (443) formed on the seed layer (442) and containing potassium, sodium, and niobium; and an upper electrode (444) formed on the piezoelectric layer (443).

Description

Technical Field

[0001] This invention relates to a piezoelectric element. Background Technology

[0002] The development of piezoelectric elements using non-lead piezoelectric materials, such as lead zirconate titanate, has been ongoing. For example, Patent Document 1 discloses a piezoelectric element having a piezoelectric layer of potassium sodium niobate (KNN). In this piezoelectric element, a bonding layer is formed between a first electrode and a vibrating plate to improve the adhesion between the first electrode and the vibrating plate. It is assumed that titanium or titanium oxide is used in the bonding layer.

[0003] However, in the piezoelectric element described in Patent Document 1, there is a problem that if the piezoelectric layer is formed to be relatively thick, cracks are easily generated in the piezoelectric layer. Specifically, KNN is a composite oxide with a perovskite structure. If titanium or titanium oxide is used in the bonding layer, titanium can easily diffuse into the piezoelectric layer through heat treatment or other processes during manufacturing. If titanium diffuses, in addition to the original KNN grains preferentially oriented on the (100) plane, KNN grains oriented on the (111) plane will also grow. Therefore, if the piezoelectric layer is formed to be relatively thick, the internal stress is easily concentrated at the grain boundaries due to the difference in shrinkage rate, which can lead to cracks being generated in the piezoelectric layer.

[0004] Furthermore, if the bonding layer is omitted or zirconium is used in the bonding layer, cracks are easily generated in the piezoelectric layer regardless of the crystal orientation. This is because, although the diffusion of titanium is reduced, the residual stress inside the piezoelectric layer caused by the difference in the coefficient of linear expansion and / or the difference in lattice spacing between the piezoelectric layer and the vibrating plate is difficult to alleviate. Therefore, a piezoelectric element is sought that suppresses the generation of cracks in the piezoelectric layer.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-133458 Summary of the Invention

[0006] The piezoelectric element comprises: a bonding layer formed on a substrate and containing titanium; a lower electrode formed on the bonding layer; a diffusion suppression layer formed on the lower electrode and containing iridium; a seed layer formed on the diffusion suppression layer and containing bismuth; a piezoelectric layer formed on the seed layer and containing potassium, sodium, and niobium; and an upper electrode formed on the piezoelectric layer. Attached Figure Description

[0007] Figure 1 This is a schematic diagram showing the outline structure of a recording device including the droplet ejection head according to the first embodiment.

[0008] Figure 2 This is an exploded 3D view of the droplet ejector.

[0009] Figure 3 For inclusion Figure 2 A schematic cross-sectional view of line segment AA along the XZ plane.

[0010] Figure 4 This is a top view showing the structure of a piezoelectric element.

[0011] Figure 5 For inclusion Figure 4 A sectional view of line segment EE along the YZ plane.

[0012] Figure 6 The X-ray diffraction intensity curves are for the examples and comparative examples.

[0013] Figure 7 The X-ray diffraction intensity curves are for the examples and comparative examples.

[0014] Figure 8 The X-ray diffraction intensity curves are for the examples and comparative examples.

[0015] Figure 9 This is a cross-sectional SEM image of the piezoelectric layer in Example 1.

[0016] Figure 10 This is a planar SEM image of the piezoelectric layer in Example 1.

[0017] Figure 11 A cross-sectional SEM image of the piezoelectric layer in Comparative Example 1.

[0018] Figure 12 A planar SEM image of the piezoelectric layer in Comparative Example 1.

[0019] Figure 13 A diagram showing the depth orientation profile of Example 1 based on SIMS measurements.

[0020] Figure 14 A diagram showing the depth-direction profile of Comparative Example 1 based on SIMS measurements.

[0021] Figure 15 A diagram showing the depth-direction profile of Comparative Example 2 based on SIMS measurements.

[0022] Figure 16 This is a schematic cross-sectional view showing the diffusion state of titanium in the piezoelectric layer of Example 1.

[0023] Figure 17 A schematic cross-sectional view showing the diffusion state of titanium in the piezoelectric layer of Comparative Example 1.

[0024] Figure 18 This is a cross-sectional view showing the structure of the droplet ejector according to the second embodiment. Detailed Implementation

[0025] 1. First Implementation Method

[0026] The embodiments described below illustrate a piezoelectric element using a lead-free piezoelectric material, a droplet ejector using the piezoelectric element, and a recording device, and will be described with reference to the accompanying drawings. In the following drawings, the XYZ axes, serving as coordinate axes, are labeled as needed, with the direction pointed to by the arrows designated as the "+" direction and the direction opposite to the "+" direction designated as the "-" direction. Sometimes the +Z direction is referred to as "up," and the -Z direction as "down," and the view from the +Z direction is sometimes referred to as a top view or a plane view. Furthermore, for ease of illustration, the sizes of the various components differ from their actual dimensions.

[0027] 1.1. Recording device

[0028] like Figure 1 As shown, the recording device 100 of the inkjet printer has a droplet ejector head 1. The droplet ejector head 1 is equipped with a piezoelectric element 44 as described in this embodiment below.

[0029] In the recording apparatus 100, ink droplets are applied to the recording medium 2 from the droplet ejection head 1, thereby performing printing such as recording. In addition to the droplet ejection head 1, the recording apparatus 100 also includes a head moving mechanism 5, a medium conveying mechanism 6, an ink receiving unit 7, and a control unit 18.

[0030] The head movement mechanism 5 includes a carriage 4 and a timing belt 8. A droplet ejector head 1 is mounted on the carriage 4. The carriage 4 is connected to the timing belt 8. The timing belt 8 is driven by a motor (not shown), causing the carriage 4 to move in the X-axis direction, which is the main scanning direction. Thus, the droplet ejector head 1 can reciprocate relative to the recording medium 2 in the X-axis direction.

[0031] The media delivery mechanism 6 delivers the recording medium 2 in the +Y direction, which is the sub-scanning direction. As a result, the recording medium 2 moves relative to the droplet ejection head 1 in the +Y direction.

[0032] The ink collection unit 7 collects the ink ejected from the droplet ejector head 1. The ink collected in the ink collection unit 7 is supplied to the droplet ejector head 1 via an ink piping (not shown). Multiple ink collection units 7 may be configured, for example, to correspond to various types of inks, such as black, cyan, magenta, and yellow. Furthermore, the droplets ejected from the droplet ejector head 1 are not limited to ink; they may also be droplets other than inks, such as processing fluids or cleaning fluids.

[0033] The droplet ejector head 1 is positioned in the carriage 4 on the side opposite to the recording medium 2. The droplet ejector head 1 has a nozzle surface (not shown) on the surface opposite to the recording medium 2. Multiple nozzles N are provided on the nozzle surface. The multiple nozzles N are arranged in a manner corresponding to the types of inks described above.

[0034] The ink in the ink collection unit 7 is supplied to the droplet ejection head 1, and is ejected in the form of droplets from multiple nozzles N by the actuator of the droplet ejection head 1, which will be described later. The ejected ink droplets fall and adhere to the recording medium 2.

[0035] The control unit 18 includes multiple processing circuits such as CPUs (Central Processing Units) or FPGAs (Field Programmable Gate Arrays), and storage circuits such as semiconductor memories. The control unit 18 controls the overall operation of the recording device 100. The head moving mechanism 5, the media conveying mechanism 6, and the droplet ejection head 1 are electrically connected to the control unit 18 and are comprehensively controlled by the control unit 18.

[0036] According to the above method, by moving the droplet ejector head 1 in the main scanning direction and corresponding to the transport of the recording medium 2 in the sub-scanning direction, and by attaching ink to the recording medium 2 at a predetermined time, it is possible to print images on the recording medium 2.

[0037] Although a serial printer is illustrated as a recording device 100 in this embodiment, the recording device using the droplet ejector head 1 is not limited to this. For example, the recording device may also be a line printhead printer. Furthermore, the device equipped with the droplet ejector head 1 is not limited to the recording device 100, and may also be, for example, a manufacturing apparatus for color filters such as liquid crystal displays, an electrode forming apparatus such as organic electroluminescent displays or field emission displays, a biochip manufacturing apparatus, etc.

[0038] 1.2. Droplet ejector

[0039] like Figure 2As shown, the droplet ejector head 1 includes: a nozzle plate 62, two vibration absorbers 64, a flow channel forming substrate 32, a pressure chamber substrate 34, multiple piezoelectric elements 44, a vibrating plate 36 serving as a substrate, a wiring substrate 46, a drive circuit 50, and a housing portion 48. The piezoelectric device 40 is thus constructed by the multiple piezoelectric elements 44.

[0040] The nozzle plate 62, the vibration absorber 64, the flow channel forming substrate 32, the pressure chamber substrate 34, the vibrating plate 36, and the wiring substrate 46 are generally rectangular plate-shaped components, with their long sides aligned along the Y-axis when viewed from above. During the manufacture of the droplet ejector head 1, the nozzle plate 62, the two vibration absorbers 64, the flow channel forming substrate 32, the pressure chamber substrate 34, the vibrating plate 36, the wiring substrate 46, and the housing portion 48 are stacked in this order and bonded together, for example, by an adhesive.

[0041] The nozzle plate 62, the flow channel forming substrate 32, the pressure chamber substrate 34, and the vibrating plate 36 have a structure that is approximately linearly symmetrical with respect to the center line in the direction along their respective X-axis. In planar view, the pressure chamber substrate 34, the vibrating plate 36, and the wiring substrate 46 are smaller in size compared to the flow channel forming substrate 32 and the housing portion 48.

[0042] Multiple nozzles N are formed on the nozzle plate 62. Each nozzle N is a through-hole penetrating the nozzle plate 62 and is approximately circular in planar shape. The multiple nozzles N are arranged along the Y-axis and in two rows along the X-axis. Two vibration absorbers 64 are configured to sandwich the nozzle plate 62 along the X-axis. The two vibration absorbers 64 are flexible thin films.

[0043] The flow channel forming substrate 32 has two first openings 32a, a plurality of second openings 32b, and a plurality of third openings 32c. The first openings 32a are approximately rectangular in shape with their long sides along the Y-axis in the plane. When viewed from above, the first openings 32a are provided along the long side of the flow channel forming substrate 32 along the Y-axis.

[0044] Multiple second openings 32b are arranged in two columns along the Y-axis. Similarly, multiple third openings 32c are also arranged in two columns along the Y-axis. Along the X-axis, a column of one first opening 32a, a column of one second opening 32b, a column of one third opening 32c, a column of one second opening 32b, and a column of the other first opening 32a are arranged in this order. Furthermore, adjacent second openings 32b and third openings 32c along the X-axis are arranged in approximately the same position along the Y-axis.

[0045] A plurality of openings 34a are provided on the pressure chamber substrate 34. Each opening 34a is approximately rectangular in shape, with its long side along the X-axis in the plane. The plurality of openings 34a are arranged in two rows along the Y-axis. The two rows of openings 34a are arranged side-by-side along the X-axis. Each opening 34a is located at a position where it overlaps in the plane with the second opening 32b and the third opening 32c adjacent to the flow channel forming substrate 32.

[0046] Multiple piezoelectric elements 44 are formed on the vibrating plate 36. Specifically, multiple piezoelectric elements 44 are disposed on the main surface above the vibrating plate 36. The multiple piezoelectric elements 44 are respectively disposed at positions that overlap with the multiple openings 34a of the pressure chamber substrate 34 when viewed from above. The various openings 34a of the pressure chamber substrate 34, together with the lower surface of the vibrating plate 36, form the pressure chamber C, which will be described later.

[0047] The drive circuit 50 drives multiple piezoelectric elements 44. Specifically, the drive circuit 50 is an IC (Integrated Circuit) chip that outputs drive signals and reference voltages to drive each piezoelectric element 44. The drive circuit 50 is mounted on the main surface above the wiring substrate 46. On the wiring substrate 46, wiring is provided for the input signals to the drive circuit 50, the drive signals output from the drive circuit 50, and the reference voltages.

[0048] Terminals (not shown) of the wiring board 46 and each piezoelectric element 44 are joined via bumps B, described later. Input signals to the drive circuit 50 are input to these terminals, for example via FPCs (Flexible Printed Circuits).

[0049] The housing 48 is a container for storing ink and is frame-shaped. When assembling the droplet ejector head 1, a pressure chamber substrate 34, a vibrating plate 36, and a wiring substrate 46 are disposed in the internal space of the housing 48. Through holes 48a are formed on both sides of the housing 48 along the X-axis direction.

[0050] like Figure 3 As shown, a wiring board 46, a vibrating plate 36, and a pressure chamber board 34 are housed inside the frame-shaped housing 48. The outer edge of the frame-shaped housing 48 is connected to the top of the flow channel forming board 32. A nozzle plate 62 and two vibration absorbers 64 are connected to the bottom of the flow channel forming board 32. Here, the droplet ejector head 1 has Figure 3The structure is symmetrical along the left and right sides. Therefore, in the following description, we will focus on the structure in the -X direction (left side), while the description of the structure in the +X direction will be omitted.

[0051] A space Rb is formed near the end of the housing portion 48 in the -X direction. The upper part of the space Rb communicates with the through hole 48a, and the lower part communicates with the first opening 32a of the flow channel forming substrate 32. The shape of the space Rb corresponds to that of the first opening 32a in the plane and extends along the Y-axis.

[0052] The flow channel forming substrate 32 includes a space Ra, a partition wall 32d, a supply flow channel 26b, and a connecting flow channel 26c. The space Ra is an internal space formed through a first opening 32a. The partition wall 32d is disposed between the first opening 32a and the second opening 32b. The lower end of the partition wall 32d is above the lower surface of the flow channel forming substrate 32 and is recessed in the +Z direction. The supply liquid chamber 26a is formed through the lower end of the partition wall 32d and the upper surface of the vibration absorber 64. The supply flow channel 26b is an internal space formed through the second opening 32b.

[0053] The pressure chamber C is formed by the opening 34a of the pressure chamber substrate 34, the surface below the vibrating plate 36, and the surface above the flow channel forming substrate 32. That is, the vibrating plate 36 forms the upper wall surface, which is part of the wall surface of the pressure chamber C. The pressure chamber C communicates with the supply flow channel 26b at the lower end in the -X direction.

[0054] The connecting flow channel 26c is an internal space formed through the third opening 32c. The pressure chamber C is connected to the connecting flow channel 26c at the lower end in the +X direction, and is connected to the nozzle N of the nozzle plate 62 via the connecting flow channel 26c.

[0055] According to the above method, the ink flow channels are connected in the above sequence from the through hole 48a to the spaces Rb, Ra, the supply liquid chamber 26a, the supply channel 26b, the pressure chamber C, the connecting channel 26c, and the nozzle N, thereby forming an ink flow channel. In the above structure for forming the ink flow channel, the supply liquid chamber 26a to the connecting channel 26c is arranged in such a way that each of the plurality of nozzles N corresponds to one of the plurality of nozzles N.

[0056] Ink from the ink receiving section 7 is supplied through the through hole 48a. Spaces Ra and Rb function as liquid storage chambers for storing ink supplied to the pressure chamber C. Space Rb communicates with a plurality of spaces Ra arranged along the Y-axis. Ink supplied from the through hole 48a is stored in space Ra via space Rb. The ink stored in space Ra is supplied to the pressure chamber C via supply liquid chamber 26a and supply flow channel 26b.

[0057] The piezoelectric element 44 is arranged on a plane in a manner that overlaps with the pressure chamber C. That is, each piezoelectric element 44 is arranged in a manner corresponding to a plurality of pressure chambers C. The piezoelectric element 44 includes the driving unit 440 described later. A wiring board 46 is disposed above the piezoelectric element 44, and a drive circuit 50 is disposed above the wiring board 46. The wiring board 46 and the piezoelectric element 44 are electrically connected by a protrusion B.

[0058] A drive signal and a reference voltage are input from the wiring board 46 to the piezoelectric element 44 via the bump B. The piezoelectric element 44 is subjected to voltage by the input drive signal and reference voltage, thereby deforming. The vibrating plate 36 vibrates in conjunction with the deformation of the piezoelectric element 44. In this way, ink is ejected from the nozzle N by pressure fluctuations within the pressure chamber C.

[0059] The vibrating plate 36 is driven by the piezoelectric element 44. The aforementioned drive circuit 50 applies a voltage to the piezoelectric element 44. In addition, the piezoelectric element 44, the vibrating plate 36 which also serves as a drive unit, and the drive circuit 50 which serves as a voltage application unit constitute an actuator for ejecting droplets.

[0060] 1.3. Piezoelectric elements

[0061] The planar configuration of the piezoelectric element 44 is described. For example... Figure 4 As shown, multiple piezoelectric elements 44 are arranged adjacent to each other in the direction along the Y-axis. Each piezoelectric element 44 includes a lower electrode 441, a seed layer 442, a piezoelectric body layer 443, and an upper electrode 444. While details will be described below, they are stacked in the order of lower electrode 441, seed layer 442, piezoelectric body layer 443, and upper electrode 444, from the vibrating plate 36 upwards in the direction along the Z-axis. Furthermore, in conjunction with... Figure 4 In the following related descriptions, unless otherwise specified beforehand, the descriptions are intended to be of the view from above.

[0062] Multiple upper electrodes 444 are arranged to overlap relative to each pressure chamber C in the direction along the Z-axis. The upper electrodes 444 extend in the +X direction from a generally rectangular region overlapping with the pressure chamber C. Although not shown in the figure, each upper electrode 444 is individually electrically connected to the aforementioned drive circuit 50 at its tip extending in the +X direction.

[0063] In the manufacturing process of the piezoelectric element 44, after the seed layer 442 and piezoelectric layer 443 are formed into a generally flat surface by covering the lower electrode 441, only region S is etched. That is, in region S, the seed layer 442 and piezoelectric layer 443 are not disposed. Region S is a generally hexagonal shape that is elongated along the X-axis and is disposed between adjacent upper electrodes 444 along the Y-axis.

[0064] The lower electrode 441 is formed as a single surface covering the insulating layer 362. The lower electrode 441 is electrically connected to the drive circuit 50 via a terminal (not shown). Independent voltages are applied to each of the upper electrodes 444, while a common voltage is applied to the lower electrode 441.

[0065] The detailed structure of the piezoelectric element 44 is described below. For example... Figure 5 As shown, multiple piezoelectric elements 44 are formed in contact with the upper surface of the vibrating plate 36. A region S is arranged between two adjacent piezoelectric elements 44 along the Y-axis. Furthermore, in Figure 5 In addition to the two piezoelectric elements 44, the diagram also shows a vibrating plate 36, a flow channel forming substrate 32, and a pressure chamber substrate 34.

[0066] The piezoelectric element 44 includes: a bonding layer 445, a lower electrode 441, a diffusion suppression layer 447, a seed layer 442, a piezoelectric body layer 443, and an upper electrode 444. In the piezoelectric element 44, the bonding layer 445, the lower electrode 441, the diffusion suppression layer 447, the seed layer 442, the piezoelectric body layer 443, and the upper electrode 444 are stacked upwards in the aforementioned order. That is, the stacking direction of each layer of the piezoelectric element 44 is along the Z-axis.

[0067] The area on the plane where the adhering layer 445, lower electrode 441, seed layer 442, diffusion suppression layer 447, piezoelectric layer 443, and upper electrode 444 overlap is designated as the active part 440. The active part 440 is the area where the piezoelectric layer 443 deforms when a voltage is applied between the lower electrode 441 and the upper electrode 444. The active part 440 is positioned opposite the pressure chamber C along the Z-axis, separated by the vibrating plate 36.

[0068] Here, the diffusion inhibition layer 447 is formed as a single surface. Alternatively, the diffusion inhibition layer 447 may also be formed discontinuously in the plane of region S.

[0069] Furthermore, seed layers 442, each corresponding to one of the plurality of piezoelectric elements 44, are formed continuously in a plane in regions other than region S. Piezoelectric body layers 443, each corresponding to one of the plurality of piezoelectric elements 44, are formed continuously in a plane in regions other than region S.

[0070] The vibrating plate 36 has a silicon (Si) substrate 361 and an insulating layer 362. The silicon substrate 361 is made of single-crystal silicon. Although not shown in the figure, the silicon substrate 361 includes a silicon layer and a silicon oxide layer (SiO2). The silicon oxide layer is disposed on top of the silicon layer and is in contact with the insulating layer 362. Alternatively, an SOI (Silicon on Insulator) substrate or a glass substrate may be used instead of the silicon substrate 361. The insulating layer 362 contains zirconium oxide (ZrO2).

[0071] An adhesive layer 445 is formed on the vibrating plate 36, specifically, it is formed at a position overlapping the plane of the active part 440 in such a way that it is in contact with the surface above the insulating layer 362. The adhesive layer 445 contains titanium (Ti). The titanium contained in the adhesive layer 445 may also be titanium derived from titanium oxide (TiO2).

[0072] Here, due to the difference in the coefficient of linear expansion or the difference in lattice spacing between the piezoelectric layer 443 and the vibrating plate 36, residual stress may be generated inside the piezoelectric layer 443. In contrast, by including titanium in the bonding layer 445, the aforementioned residual stress can be easily alleviated. Alternatively, zirconium or zinc (Zn) may be used instead of titanium in the bonding layer 445.

[0073] The lower electrode 441 is formed on the bonding layer 445, specifically in contact with the upper surface of the bonding layer 445. The lower electrode 441 comprises platinum (Pt). The lower electrode 441 is not limited to being composed of a monolayer of platinum; for example, it can be composed of IrO. x The conductive oxide film can be composed of a single layer of materials such as LaNiO3 and SrRuO3, or it can be composed of two or more layers of the above materials stacked together.

[0074] The diffusion suppression layer 447 is formed as a whole surface covering the lower electrode 441. More specifically, it is formed to cover a portion of the adhering layer 445 and the sides of the lower electrode 441, the top of the lower electrode 441, and the top of the vibrating plate 36 on both sides of the adhering layer 445. In other words, the diffusion suppression layer 447 is located between the adhering layer 445 and the lower electrode 441 and the seed layer 442 and the piezoelectric layer 443. Therefore, even at the interface between the diffusion suppression layer 447 and the vibrating plate 36, the diffusion of titanium can be suppressed.

[0075] The diffusion inhibition layer 447 contains iridium (Ir). This suppresses the diffusion of titanium contained in the adjacent layer 445 with respect to the piezoelectric layer 443. The diffusion inhibition layer 447 may also contain iridium oxide (IrO). x Iridium oxide can sometimes be generated during heat treatment or other processes in the manufacturing of piezoelectric element 44 due to the oxidation of iridium.

[0076] Although the thickness of the diffusion inhibition layer 447 is not specifically limited, it is set to, for example, 3 nm to 50 nm.

[0077] A seed layer 442 is formed on the diffusion suppression layer 447, specifically, in a manner that covers the diffusion suppression layer 447. The seed layer 442 is controlled in a way that ensures the crystal orientation of the composite oxide in the piezoelectric layer 443 is consistent. Through the seed layer 442, the preferential orientation of the crystal of the piezoelectric layer 443 toward the (100) plane can be promoted.

[0078] Seed layer 442 is a composite oxide containing bismuth (Bi), titanium (Ti), iron (Fe), and lead (Pb) and having a perovskite structure. Although seed layer 442 contains titanium, which could potentially facilitate the growth of KNN grains oriented towards the (111) plane in piezoelectric layer 443, the applicant's research found that crystal orientation towards the (100) plane was promoted in the composite oxide of piezoelectric layer 443. Therefore, the generation of cracks caused by grain boundaries can be further suppressed, and the electrical properties of piezoelectric element 44 are improved.

[0079] Although the composition of each element in the seed layer 442 is not specifically limited, for example, lead is set to 0.1, bismuth to 1.1, iron to 0.5, titanium to 0.5, and oxygen (O) to 3.0 in molar ratios of each element. These components are adjusted, for example, by the molar ratios of each element in the precursor solution of the seed layer 442 during its fabrication. Because the seed layer 442 has a relatively high dielectric constant, the displacement efficiency, expressed as the displacement of the piezoelectric layer 443 relative to the applied voltage, is good. The method for manufacturing the piezoelectric element 44 will be described below.

[0080] The thickness of the seed layer 442 is 20 nm or less. Therefore, since the seed layer 442 contains bismuth, iron, titanium, and lead, even with a thickness of 20 nm or less, the effect of ensuring uniform crystal orientation of the composite oxide can be guaranteed. Furthermore, because the thickness is thinner, the diffusion of titanium contained in the seed layer 442 is reduced compared to the piezoelectric layer 443.

[0081] Furthermore, seed layer 442 is not limited to a perovskite structure. Seed layer 442 can also be a structure similar to that of perovskite, thus employing an octahedral crystal structure with six oxygen atoms coordinated in iron or titanium.

[0082] The piezoelectric layer 443 is the main part of the piezoelectric element 44, which has piezoelectric properties and is deformed by the application of voltage. The piezoelectric layer 443 is formed on the seed layer 442 in a connected manner and covers the top of the seed layer 442. The piezoelectric layer 443 contains potassium (K), sodium (Na) and niobium (Nb), and is mainly composed of a composite oxide having a perovskite structure represented by the general formula ABO3. In detail, the above-mentioned composite oxide can be represented by the following formula (1).

[0083] (K m Na 1-m NbO3…(1)

[0084] Equation (1) satisfies 0.1≤m≤0.9.

[0085] The potassium sodium niobate composite oxide of formula (1) is a non-lead piezoelectric material with suppressed lead and other content, and is a so-called KNN-type composite oxide. KNN-type composite oxides are beneficial for reducing environmental impact and have superior piezoelectric properties compared to other non-lead piezoelectric materials. Furthermore, since KNN-type composite oxides have a higher Curie temperature than other non-lead piezoelectric materials such as BNT-BKT-BT, and are less prone to depolarization caused by temperature rise, they are advantageous for use at high temperatures.

[0086] In formula (1), preferably, the potassium content is set to a molar percentage of 30% or more and 70% or less relative to the total amount of metal elements constituting the A site of ABO3. That is, preferably, m satisfies 0.3 ≤ m ≤ 0.7. More preferably, the potassium content is set to a molar percentage of 40% or more and 60% or less relative to the total amount of metal elements constituting the A site. That is, more preferably, m satisfies 0.4 ≤ m ≤ 0.6. Accordingly, the piezoelectric properties of the piezoelectric layer 443 are improved.

[0087] In addition to the KNN-type composite oxide of formula (1), the piezoelectric layer 443 may also contain lithium and other metal elements such as the first transition element. Furthermore, the piezoelectric layer 443 may also contain a piezoelectric material comprising a composite oxide having a perovskite structure represented by the general formula ABO3, containing potassium, sodium, and niobium, and a mixed crystal of other composite oxides having a perovskite structure represented by the general formula ABO3. Furthermore, the piezoelectric material contained in the piezoelectric layer 443 may also contain elements among the aforementioned elements that have partially missing components or elements that have partially excess components.

[0088] The piezoelectric layer 443 has a crystal orientation in the {100} orientation. That is, the piezoelectric layer 443 is preferentially oriented on the (100) plane. This can further improve the piezoelectric characteristics of the piezoelectric element 44. Here, in this specification, "preferential orientation" means that 50% or more, preferably 80% or more of the crystals are oriented on a predetermined crystal plane. Specifically, "preferential orientation on the (100) plane" includes the case where all the crystals of the piezoelectric layer 443 are oriented on the (100) plane, and the case where at least 50% or more of the crystals are oriented on the (100) plane. The crystal orientation of the piezoelectric layer 443 can be determined by analyzing the X-ray diffraction intensity curve of X-ray diffraction (XRD).

[0089] Although the thickness of the piezoelectric layer 443 is not specifically limited, it is, for example, set to 500 nm to 2000 nm.

[0090] Here, for the piezoelectric layer 443, when the elemental concentration in the depth direction is measured from the upper surface using secondary ion mass spectrometry (SIMS), the detected titanium intensity slightly increases on the side of the lower, closely attached layer 445. In this embodiment, the diffusion of titanium is suppressed by the diffusion suppression layer 447. Therefore, in the piezoelectric layer 443, in the region where the distance from the seed layer 442 in the stacking direction, i.e., the distance along the Z-axis, is 240 nm or more, the titanium intensity measured by SIMS is 300 cps or less. Thus, the orientation of the crystal in the piezoelectric layer 443 to surfaces other than the intended (111) plane can be further suppressed.

[0091] An upper electrode 444 is formed on a piezoelectric layer 443. The upper electrode 444 is disposed on the piezoelectric layer 443. The upper electrode 444 is made of a platinum layer. The upper electrode 444 is not limited to being made of a platinum layer; for example, it can be a single layer of a metallic material such as aluminum, nickel, gold, or copper, or a structure in which two or more single layers of the aforementioned metallic materials are stacked.

[0092] Furthermore, although this embodiment illustrates a piezoelectric element 44 in which a lower electrode 441, a seed layer 442, a piezoelectric layer 443, and an upper electrode 444 are sequentially stacked on a vibrating plate 36, it is not limited to this. The piezoelectric element of the present invention may also be a longitudinally vibrating type piezoelectric element in which piezoelectric materials and electrode forming materials are alternately stacked to stretch and contract in the axial direction.

[0093] 1.4. Manufacturing Method of Piezoelectric Elements

[0094] First, the vibrating plate 36 is fabricated. Specifically, the silicon plate is thermally oxidized to form silicon oxide on the upper surface. This forms a silicon substrate 361 comprising a silicon layer and a silicon oxide layer. Next, after the silicon oxide layer is coated with a zirconium layer by sputtering, the zirconium layer is thermally oxidized to form a zirconium oxide layer as an insulating layer 362.

[0095] Next, the bonding layer 445 and the lower electrode 441 are formed. Specifically, a titanium layer, a platinum layer, and then an iridium-containing layer are stacked in this order on the surface above the insulating layer 362 by sputtering.

[0096] Next, a seed layer 442 is formed using the MOD (Metal Organic Decomposition) method. Specifically, a propionic acid solution of lead, bismuth, iron, and titanium is prepared as the precursor solution for the seed layer 442. The molar ratio of each element is set, for example, to be lead:bismuth:iron:titanium = 10:110:50:50. The propionic acid solution is then spin-coated onto the diffusion inhibition layer 447.

[0097] After drying and degreasing at 350°C using a hot plate, the material is then subjected to RTA (Rapid Thermal Annealing) using an infrared lamp or similar device, resulting in a three-minute heat treatment at 650°C in an oxygen atmosphere. This forms a full-surface layer containing a seed layer 442.

[0098] Next, the piezoelectric layer 443 is formed using the MOD method. First, a precursor solution for the above layer is prepared. This precursor solution contains, as a solute, metal complexes of the elements contained in the piezoelectric layer 443 described above, such as potassium, sodium, and niobium. The solvent for the precursor solution is an organic solvent capable of dissolving or dispersing the metal complexes.

[0099] Specifically, potassium 2-ethylhexanoate, sodium 2-ethylhexanoate, niobium 2-ethylhexanoate, etc., are used as the aforementioned metal complexes. In the solvent, organic solvent monomers or mixtures such as 2-n-butoxyethanol or n-octane are used, for example. The content of each metal complex in the aforementioned precursor solution corresponds to the desired molar ratio of each element in the piezoelectric layer 443.

[0100] The precursor solution was coated onto the layer containing seed layer 442 using spin coating. Next, after drying at 180°C using a hot plate and degreasing at 380°C, a heat treatment was performed at 750°C for three minutes in an oxygen atmosphere using RTA. This promoted the crystallization of the composite oxide of piezoelectric layer 443. A full-surface layer containing piezoelectric layer 443 was then formed. To ensure the thickness of piezoelectric layer 443, the coating process from precursor solution application to the heat treatment performed by RTA was repeated.

[0101] In conventional piezoelectric elements, the diffusion of titanium is promoted by heating the precursor solution of the piezoelectric layer. Repeated application of the precursor solution followed by heating further promotes titanium diffusion. In contrast, in the piezoelectric element 44 of this embodiment, the diffusion of titanium into the piezoelectric layer 443 is suppressed by the diffusion suppression layer 447.

[0102] Furthermore, the fabrication method for the seed layer 442 and the piezoelectric layer 443 is not limited to the MOD method. Known methods such as the vapor phase method can be used in the fabrication of the piezoelectric layer 443.

[0103] Next, a layer that becomes the upper electrode 444 is formed. Specifically, a platinum layer is formed as a whole surface on the surface above the layer that becomes the piezoelectric layer 443 by sputtering.

[0104] Next, region S is set by patterning. Specifically, in the layer containing seed layer 442, the layer that becomes piezoelectric layer 443, and the layer that becomes upper electrode 444, the region corresponding to region S is removed, thereby forming seed layer 442, piezoelectric layer 443, and upper electrode 444. Methods for patterning include dry etching such as reactive ion etching or ion polishing, and wet etching using an etchant. Through these methods, piezoelectric element 44 can be manufactured.

[0105] According to this embodiment, the following effects can be obtained.

[0106] Crack formation can be suppressed in the piezoelectric layer 443. Specifically, by using the diffusion suppression layer 447 containing iridium, the diffusion of titanium from the bonding layer 445 into the piezoelectric layer 443 can be suppressed. Therefore, grains oriented on unintended surfaces become difficult to grow in the piezoelectric layer 443. Furthermore, the difference in the coefficients of linear expansion between the piezoelectric layer 443 and the vibrating plate 36 is easily mitigated compared to the case where a bonding layer without titanium is formed or the bonding layer 445 is omitted. In these ways, even if the piezoelectric layer 443 is formed relatively thickly, crack formation is less likely. Therefore, a piezoelectric element 44 that suppresses crack formation in the piezoelectric layer 443 can be provided.

[0107] 2. Examples and Comparative Examples

[0108] The following examples and comparative examples are shown, and the effects of the above-described embodiments will be explained in more detail. Regarding Example 1 and Comparative Examples 1 to 4, the structure of the piezoelectric element and the evaluation results will be shown in Table 1.

[0109] Table 1

[0110]

[0111] In addition, in the piezoelectric element structures in Table 1, the thickness of the layers other than the piezoelectric layer is shown in parentheses (), and the number of layers in the piezoelectric layer is shown in parentheses <>. In the Ti diffusion column of the evaluation results in Table 1, layers with titanium strength exceeding 200 cps as measured by SIMS are shown.

[0112] 2.1. Manufacturing of piezoelectric elements

[0113] In the piezoelectric elements of Example 1 and Comparative Examples 1 to 4, the molar ratio of each element contained in the seed layer was set to bismuth:iron:titanium:lead = 110:50:50:10. Furthermore, the molar ratio of each element contained in the piezoelectric layer was set to potassium:sodium = 51:49, and the ratio of the element disposed at site A to the element disposed at site B was set to 107:100. Additionally, the main element disposed at site A was potassium or sodium, and the main element disposed at site B was niobium.

[0114] In Example 1, the insulating layer 362 of the vibrating plate 36, the bonding layer 445, the diffusion suppression layer 447, the seed layer 442, and the piezoelectric layer 443 are stacked and manufactured using the above-described manufacturing method. The piezoelectric layer 443 is stacked in 10 layers by repeatedly applying a precursor solution until heat treatment. Furthermore, in this evaluation, since measurements of electrical characteristics, etc., were not performed, the formation of the upper electrode 444 is omitted.

[0115] In Comparative Example 1, compared to Example 1, an additional layer made of titanium was formed between the diffusion inhibition layer and the seed layer using the same method as the adhering layer 445. The piezoelectric layer was repeatedly laminated after heat treatment until cracks appeared. Furthermore, the repeated lamination was also performed in Comparative Examples 2, 3, and 4 below.

[0116] In Comparative Example 2, everything was set up the same as in Example 1 except that the bonding layer 445 was omitted. In Comparative Example 3, everything was set up the same as in Example 1 except that the diffusion suppression layer 447 was omitted. In Comparative Example 4, everything was set up the same as in Comparative Example 3 except that the bonding layer was a zirconium layer and the thickness was set to 10 nm.

[0117] 2.2 Evaluation of piezoelectric elements

[0118] 2.2.1. Crack Formation

[0119] The surface above the piezoelectric layer was observed using a metal microscope to investigate the presence or absence of cracks. The results showed that in Example 1, no cracks occurred even when 10 layers of piezoelectric layer 443 were stacked with a thickness of 790 nm. In Comparative Example 1, cracks occurred when 10 layers of piezoelectric layer were stacked with a thickness of 790 nm. In Comparative Example 2, cracks occurred when 7 layers of piezoelectric layer were stacked with a thickness of 540 nm. In Comparative Example 3, cracks occurred when 9 layers of piezoelectric layer were stacked with a thickness of 670 nm. In Comparative Example 4, cracks occurred when 6 layers of piezoelectric layer were stacked with a thickness of 450 nm. Furthermore, in Example 1, no cracks occurred even when 15 layers of piezoelectric layer 443 were stacked with a thickness of 1200 nm.

[0120] Based on the above, it is shown that in Example 1, even if the piezoelectric layer 443 is formed to be relatively thick, crack formation can be suppressed. In contrast, in Comparative Examples 1 to 4, it was found that if the piezoelectric layer is formed to be relatively thick, cracks are more likely to form.

[0121] 2.2.2. Analysis of Crystal Orientation

[0122] Each piezoelectric layer was measured using X-ray diffraction. The orientation to the (100), (111), and (110) planes was investigated using X-ray diffraction intensity curves. Specifically, a Bruker D8 DISCOVER with GADDS was used as the X-ray diffraction apparatus. The measurement conditions were set as follows: tube voltage 50 kV, tube current 100 mA, detector distance 15 cm, collimator diameter 0.3 mm, and measurement time 120 seconds. Furthermore, for the (111) plane, the silicon substrate was tilted at 54.74° for measurement.

[0123] For the obtained two-dimensional data, the 2θ range was set to 20°~50°, the x range to -95°~-85°, the step size to 0.02°, and the intensity normalization method to Bin normalized using the software attached to the device, thereby converting it into an X-ray diffraction intensity curve. The range corresponding to the (100) plane of KNN was then set in... Figure 6 The enlarged view shows that the range corresponding to surface (111) is similarly shown in [the image]. Figure 7 The enlarged view shows that the range corresponding to plane (110) is similarly shown in [the image]. Figure 8 The image is enlarged in the middle. Figures 6 to 8 In the diagram, the horizontal axis represents the diffraction angle 2θ (degree) of the X-rays, and the vertical axis represents the diffraction intensity.

[0124] like Figures 6 to 8 As shown, no peak values ​​were found on the (111) and (110) planes in Examples 1, 2, and 4, indicating that the orientation is preferentially oriented on the (100) plane. In contrast, peak values ​​were found on the (111) and (110) planes in Comparative Examples 1 and 3, and the half-width of the peak value on the (100) plane was wider than that on the (100) plane in Examples 1, 2, and 4. Therefore, Comparative Examples 1 and 3 are mixed crystals.

[0125] 2.2.3. Observation of grain boundaries

[0126] The grain boundaries of the piezoelectric layer were observed. Specifically, cross-sections along the Z-axis and the overlying surface of the piezoelectric layer were observed using a Hitachi High Technology Holdings S-4700 scanning electron microscope. Figure 9 as well as Figure 10 The image shows an SEM photograph of Example 1. Figure 11 as well as Figure 12 The image shown is a SEM image of Comparative Example 1.

[0127] In Example 1, as Figure 9 as well as Figure 10 As shown, no grain boundaries were found on the piezoelectric layer 443. In contrast, in Comparative Example 1, as... Figure 11 as well as Figure 12 As shown, grain boundaries, indicated by dashed triangular lines, were observed. Combined with the X-ray diffraction results described above, it can be seen that a triangular pyramidal region oriented on the (111) plane was generated in Comparative Example 1. Therefore, in Comparative Example 1, cracks may have formed along the grain boundaries. Furthermore, although the illustrations are omitted, the same observations were made for Comparative Examples 2, 3, and 4, and no grain boundaries were observed in Comparative Examples 2 and 4, while grain boundaries were observed in Comparative Example 3.

[0128] 2.2.4. Analysis of Titanium Diffusion in Piezoelectric Layers

[0129] For the piezoelectric layers of Example 1, Comparative Example 1, and Comparative Example 2, compositional analysis was performed by SIMS from the surface above the piezoelectric layer toward the seed layer depth direction, i.e., the -Z direction.

[0130] The SIMS device used was a sector-type SIMS IMS-7f from CAMECA. During the measurement, 15 kV cesium ions (Cs+) were used as the primary ions. A beam current of 10 nA was applied to a 100 μm square grating scan, and negative secondary ions were detected from the center at a 33 μm φ. An electron gun was used to suppress charging during the measurement.

[0131] exist Figures 13 to 15 The obtained depth-direction profile is shown. Additionally, for clarity, the profiles of oxygen and zirconium, etc., are omitted from the diagram. Figures 13 to 15 In the diagram, the horizontal axis represents the time (s: seconds) for tunneling in the depth direction, which can be considered as the distance from the surface above the piezoelectric layer towards the -Z direction. The vertical axis represents the detection intensity (in cps) of each element. Furthermore, for Example 1 and Comparative Example 1, in Figure 16 as well as Figure 17 The diagram shows the diffusion state of titanium inferred from SIMS analysis. Figure 16 as well as Figure 17 The diagram omits the structures other than the insulating layer 362 (zirconia), the lower electrode 441 (Pt), and the piezoelectric layer 443 (KNN).

[0132] exist Figures 13 to 15 In the figures, dashed line B indicates the boundary at a distance of 240 nm from the stacking direction of the seed layer, i.e., the +Z direction. That is, in each figure, the region to the left of dashed line B constitutes the region at a distance greater than 240 nm. Furthermore, an × symbol is used to indicate the titanium strength within dashed line B.

[0133] Furthermore, the dashed line B is determined based on the number of peak values ​​for titanium and sodium. Specifically, when piezoelectric layers are repeatedly stacked using the MOD method, in each monolayer, from the seed layer towards the +Z direction, the intensity of sodium gradually decreases from its peak value, while the intensity of potassium gradually increases from its minimum to its peak value. Therefore, in each monolayer of the piezoelectric layer, the peak position of sodium and the trough position of potassium become the interface on the seed layer side, and the trough position of sodium and the peak position of potassium become the interface in the +Z direction. Since the thickness of each of these monolayers is approximately 80 nm, the interface in the +Z direction of the third layer, extending upwards from the seed layer side of the piezoelectric layer, is defined as dashed line B. Furthermore, the method for determining the boundary of dashed line B is not limited to the method described above; in piezoelectric layers fabricated using methods such as vapor phase methods, it can also be determined through cross-sectional elemental analysis and distance measurement, for example.

[0134] like Figure 13 As shown, in Example 1, the rightmost peak position of sodium forms the interface between piezoelectric layer 443 and seed layer 442, and piezoelectric layer 443 is located to the left of this interface. In Example 1, the diffusion of titanium into piezoelectric layer 443 is very slight. Specifically, the titanium intensity at dashed line B is 70 cps, and in the region where the distance from the seed layer 442 in the stacking direction is greater than 240 nm, i.e., to the left of dashed line B, the titanium intensity is less than 300 cps. The figure schematically illustrates the above results. Figure 16 .

[0135] like Figure 16 As shown, the piezoelectric layer 443 of KNN is formed by stacking layers 443-1, 443-2, 443-3, ..., 443-10 during manufacturing. In the piezoelectric layer 443, there is almost no titanium diffusion above the third layer 443-3, which is three layers from the lower electrode 441 side. Therefore, the piezoelectric layer 443 is preferentially oriented on the (100) plane, thereby suppressing the generation of cracks.

[0136] like Figure 14 As shown, even in Comparative Example 1, the rightmost peak position of sodium becomes the interface between the piezoelectric layer and the seed layer, and the piezoelectric layer is to the left of this interface. In Comparative Example 1, the diffusion of titanium into the piezoelectric layer is more significant compared to Example 1. Specifically, the titanium strength at dashed line B is 3000 cps, and in the region to the left of dashed line B, the titanium strength exceeds 300 cps. The figure schematically illustrates the above structure. Figure 17 .

[0137] like Figure 17As shown, the piezoelectric layer KNN is formed by stacking layers KNN-1, KNN-2, ..., KNN-10 during manufacturing. In the KNN layer, titanium diffusion also extends to the tenth layer, KNN-10, starting from the Pt layer side. Consequently, the KNN layer does not preferentially align on the (100) plane, resulting in a region Q oriented on the (111) plane. Therefore, cracks CR are easily generated along the grain boundaries.

[0138] like Figure 15 As shown, even in Comparative Example 2, the rightmost peak position of sodium becomes the interface between the piezoelectric layer and the seed layer, and the piezoelectric layer is to the left of this interface. Although the diffusion of titanium into the piezoelectric layer in Comparative Example 2 is increased compared to Example 1, it is slight compared to Comparative Example 1. Specifically, the titanium intensity at dashed line B is 300 cps, and in the region to the left of dashed line B, the titanium intensity is less than 300 cps. The titanium detected in the piezoelectric layer originates from the titanium contained in the seed layer. Although the diffusion of titanium is slight in Comparative Example 2, cracks sometimes occur due to the lack of a tightly bonded layer.

[0139] Furthermore, although the illustration is omitted, the same SIMS-based analysis was performed on the piezoelectric layer of Comparative Example 3 as described above, and the results showed that the titanium strength exceeded 200 cps in the region at a distance of 240 nm or more from the stacking direction of the seed layer. Therefore, the piezoelectric layer of Comparative Example 3 was not preferentially oriented on the (100) plane, and cracks were easily generated along the grain boundaries.

[0140] 3. Second Implementation Method

[0141] Although in the above embodiment, the lower electrode 441a is formed as a whole surface covering the insulating layer 362, and the upper electrode 444a is arranged to overlap with each pressure chamber C in the direction along the Z-axis, in the second embodiment, the lower electrode 441a may also be arranged to overlap with each pressure chamber C in the direction along the Z-axis, and the upper electrode 444a may be formed as a whole surface covering the insulating layer 362.

[0142] The detailed structure of the piezoelectric element 44a will be described. Points identical to those in the first embodiment will be omitted from the description. Figure 18 As shown, multiple piezoelectric elements 44a are formed in contact with the upper surface of the vibrating plate 36. A region S is arranged between two adjacent piezoelectric elements 44 along the Y-axis direction. Furthermore, in Figure 18 In addition to the two piezoelectric elements 44a, the diagram also shows a vibrating plate 36, a flow channel forming substrate 32, and a pressure chamber substrate 34.

[0143] The piezoelectric element 44a includes: a bonding layer 445a, a lower electrode 441a, a diffusion suppression layer 447a, a seed layer 442a, a piezoelectric body layer 443a, and an upper electrode 444a. In the piezoelectric element 44a, the bonding layer 445a, the lower electrode 441a, the diffusion suppression layer 447a, the seed layer 442a, the piezoelectric body layer 443a, and the upper electrode 444a are stacked upwards in the aforementioned order. That is, the stacking direction of each layer of the piezoelectric element 44a is along the Z-axis.

[0144] The region on the plane where the adhering layer 445a, lower electrode 441a, seed layer 442, diffusion suppression layer 447a, piezoelectric layer 443a, and upper electrode 444a overlap is designated as the active part 440a. The active part 440a is the region where the piezoelectric layer 443a deforms when a voltage is applied between the lower electrode 441a and the upper electrode 444a. The active part 440a is positioned opposite the pressure chamber C, separated by the vibrating plate 36, along the Z-axis.

[0145] The bonding layer 445a is arranged to overlap with each pressure chamber C in the direction along the Z-axis. The bonding layer 445a is in contact with the surface above the insulating layer 362 on the vibrating plate 36.

[0146] The lower electrode 441a is formed in such a way that it covers a portion of the insulating layer 362 above and to the sides of the adhering layer 445a, and on both sides of the adhering layer 445a. The lower electrode 441a extends in a +X direction from a generally rectangular region overlapping the pressure chamber C. Although not shown in the figure, each lower electrode 441a is individually electrically connected to the drive circuit 50 described above at its tip extending in the +X direction.

[0147] The diffusion inhibition layer 447a is formed in a manner that is in contact with the surface above the lower electrode 441a.

[0148] The seed layer 442a is formed in such a way that it covers a portion of the area above the diffusion suppression layer 447a, both sides of the lower electrode 441a, and the area above the vibrating plates 36 on both sides of the lower electrode 441a. The seed layer 442a is controlled in such a way that the crystal orientation of the composite oxide in the piezoelectric layer 443a is consistent. The seed layer 442a promotes the preferential orientation of the crystal of the piezoelectric layer 443a toward the (100) plane.

[0149] The lower electrode 441a is located on both sides of the bonding layer 445a, between the bonding layer 445a, the seed layer 442a, and the piezoelectric layer 443a. Therefore, even at the interface between the piezoelectric layer 443a, the bonding layer 445a, and the vibrating plate 36, the diffusion of titanium is suppressed.

[0150] When the lower electrode of the piezoelectric element is configured separately, in a structure where the lower electrode does not cover the side of the bonding layer, a seed layer exists only in the middle between the side of the bonding layer and the piezoelectric layer. Therefore, in the piezoelectric layer 443a, it is possible for grains with unintended surface orientation to grow. To address this, by having the lower electrode 441a of the piezoelectric element 44a in the second embodiment cover the side of the bonding layer 445a, the diffusion of titanium from the bonding layer 445a into the piezoelectric layer 443a is suppressed. As a result, even if the piezoelectric layer 443a is formed relatively thickly, cracks are less likely to occur. Therefore, it is possible to provide a piezoelectric element 44a that suppresses the generation of cracks in the piezoelectric layer 443a.

[0151] 4. Third Implementation Method

[0152] Although the droplet ejector head 1 and the recording device 100 using the piezoelectric element 44 are illustrated in the above embodiments, the application of the piezoelectric element of the present invention is not limited thereto. The piezoelectric element of the present invention can be applied to ultrasonic sensors, piezoelectric motors, ultrasonic transformers, vibratory dust collectors, piezoelectric transducers, ultrasonic transmitters, pressure sensors, and accelerometers, etc.

[0153] Furthermore, the piezoelectric element of the present invention can also be mounted on a power generation device. Examples of power generation devices include those utilizing the piezoelectric conversion effect, those utilizing electrons generated by light, those utilizing electrons generated by heat, and those utilizing vibration.

[0154] Furthermore, the piezoelectric element of the present invention can also be applied to thermoelectric devices such as infrared detectors, terahertz detectors, temperature sensors, and thermal sensors, or to ferroelectric elements such as ferroelectric memories.

[0155] Symbol Explanation

[0156] 36… Vibrating plate as substrate; 44… Piezoelectric element; 441… Lower electrode; 442… Seed layer; 443… Piezoelectric layer; 444… Upper electrode; 445… Adhesive layer; 447… Diffusion suppression layer.

Claims

1. A piezoelectric element comprising: An adhesion layer, which is formed on the substrate, contains titanium; The lower electrode is formed on the bonding layer; A diffusion inhibition layer, which is formed on the lower electrode, contains iridium; A seed layer, which is formed on the diffusion inhibition layer, contains bismuth; A piezoelectric layer is formed on the seed layer and contains potassium, sodium, and niobium; The upper electrode is formed on the piezoelectric layer. In the piezoelectric layer, in the region where the distance from the stacking direction of the seed layer is 240 nm or more, the titanium strength measured by SIMS is less than 300 cps.

2. The piezoelectric element as claimed in claim 1, wherein, The seed layer contains iron, titanium, and lead.

3. The piezoelectric element as described in claim 2, wherein, The thickness of the seed layer is less than 20 nm.

4. The piezoelectric element according to any one of claims 1 to 3, wherein, The diffusion inhibition layer contains iridium oxide.

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