Piezoelectric element and piezoelectric element application device

Abstract

A piezoelectric element capable of suppressing generation of a crack and a piezoelectric element application device are provided. The piezoelectric element of the present application includes: a substrate including silicon; a first electrode formed on the substrate; a piezoelectric layer formed on the first electrode and including potassium, sodium, and niobium; and a second electrode formed on the piezoelectric layer, wherein a first diffusion suppression layer including an insulating material is disposed between the substrate and the piezoelectric layer, and the piezoelectric layer is continuously formed on a first region, a second region, and a third region, the first region being a surface of the first electrode, the second region being a surface of the first diffusion suppression layer, and the third region being a surface of the substrate, the third region being disposed between the first region and the second region.

Description

Technical Field

[0001] This invention relates to a piezoelectric element and a device for applying the piezoelectric element. Background Technology

[0002] Piezoelectric elements typically consist of a substrate, a piezoelectric layer with electromechanical conversion properties, and two electrodes that clamp the piezoelectric layer. In recent years, the development of devices using such piezoelectric elements as driving sources (piezoelectric element application devices) has been booming. Examples of piezoelectric element application devices include liquid jet heads (represented by inkjet recording heads), MEMS elements (represented by piezoelectric MEMS components), ultrasonic measurement devices (represented by ultrasonic sensors), and piezoelectric actuator devices.

[0003] Lead zirconate titanate (PZT) is known as a material for the piezoelectric layer of a piezoelectric element. However, in recent years, from the perspective of reducing environmental impact, the development of non-lead-based piezoelectric materials with reduced lead content has been promoted.

[0004] As one of the non-lead-based piezoelectric materials, potassium sodium niobate (KNN; (K, Na)NbO3) has been proposed, for example, as in Patent Document 1.

[0005] Specifically, Patent Document 1 discloses a piezoelectric element comprising a first electrode, a second electrode, and a thin-film piezoelectric layer disposed between the first and second electrodes, and composed of a perovskite-type composite oxide containing potassium, sodium, and niobium. Furthermore, Patent Document 1 discloses a vibrating plate composed of an elastic membrane and an insulating membrane, wherein the elastic membrane is formed on a substrate and is composed of silicon dioxide, and the insulating membrane is formed on the elastic membrane and is composed of zirconium oxide.

[0006] As mentioned above, piezoelectric elements using KNN (KNN-based piezoelectric elements) have been proposed to date as one of the non-lead-based piezoelectric materials. However, in existing KNN-based piezoelectric elements, cracks sometimes form at the interface between the insulating film constituting the vibrating plate, the first electrode, and the piezoelectric layer, allowing foreign matter such as water to potentially intrude into these cracks. During the manufacturing process of the piezoelectric element, if foreign matter such as water intrudes into these cracks, leakage current may occur. Furthermore, with the driving of the piezoelectric element, stress concentrates on these cracks, potentially causing the piezoelectric element to break.

[0007] Furthermore, if a crack is formed at the interface between the insulating film, the first electrode, and the piezoelectric layer, the material constituting the second electrode may penetrate into the crack and become conductive when the second electrode is formed on the upper part of the piezoelectric layer.

[0008] Given this situation, there is a need for a KNN-based piezoelectric element that can suppress the formation of cracks.

[0009] Furthermore, this problem is not limited to piezoelectric actuators used in liquid ejector heads, such as inkjet printheads, but also exists in piezoelectric elements used in other piezoelectric applications.

[0010] Patent Document 1: Japanese Patent Application Publication No. 2018-133458 Summary of the Invention

[0011] To address the aforementioned issues, according to one aspect of the present invention, a piezoelectric element is provided, comprising: a substrate comprising silicon; a first electrode formed on the substrate; a piezoelectric layer formed on the first electrode and comprising potassium, sodium, and niobium; a second electrode formed on the piezoelectric layer; and a first diffusion suppression layer comprising an insulating material disposed between the substrate and the piezoelectric layer. The piezoelectric layer is continuously formed on a first region, a second region, and a third region, wherein the first region is the surface of the first electrode, the second region is the surface of the first diffusion suppression layer, the third region is the surface of the substrate, and the third region is disposed between the first region and the second region.

[0012] According to another aspect of the present invention, a piezoelectric element application device may be provided, the piezoelectric element application device having a piezoelectric element of the above-described manner. Attached Figure Description

[0013] Figure 1 This is a perspective view showing the outline structure of the recording device according to Embodiment 1.

[0014] Figure 2 for Figure 1 An exploded perspective view of the recording head of the recording device.

[0015] Figure 3 for Figure 1 A top view of the recording head of the recording device.

[0016] Figure 4 for Figure 1 A cross-sectional view of the recording head of the recording device.

[0017] Figure 5 for Figure 4 Enlarged sectional view of the BB' line.

[0018] Figure 6 This is a cross-sectional view showing the piezoelectric element of Modified Example 1.

[0019] Figure 7This is a cross-sectional view showing the piezoelectric element of Modified Example 2.

[0020] Figure 8 This is a graph showing the measurement results of the secondary ion mass spectrometry analysis in Example 1.

[0021] Figure 9 A graph showing the measurement results of the secondary ion mass spectrometry analysis in Comparative Example 1. Detailed Implementation

[0022] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The following description is an illustration of one aspect of the invention, which can be modified freely without departing from the spirit of the invention. Furthermore, components marked with the same symbols in the various drawings represent the same components, and descriptions are appropriately omitted. Numbers following the text constituting a reference symbol are referenced by reference symbols containing the same text, and are used to distinguish elements having the same structure from one another. When it is not necessary to distinguish elements represented by reference symbols containing the same text from one another, these elements are each referenced by reference symbols containing only text.

[0023] In the accompanying drawings, X, Y, and Z represent three mutually orthogonal spatial axes. In this specification, the directions along these axes are designated as the first direction X (X direction), the second direction Y (Y direction), and the third direction Z (Z direction), respectively. The direction pointed to by the arrows in each drawing is designated as positive (+), and the opposite direction is designated as negative (-). The X and Y directions represent the in-plane directions of the plates, layers, and films, while the Z direction represents the thickness direction or stacking direction of the plates, layers, and films.

[0024] Furthermore, structural elements shown in the various figures, i.e., the shape and size of each part, plate, layer and film thickness, relative positional relationships, repeating units, etc., are sometimes exaggerated in the context of describing the invention. Also, the term "above" in this specification is not intended to limit the positional relationship of structural elements to "directly above". For example, expressions such as "first electrode on the substrate" or "piezoelectric layer on the first electrode" as used later do not exclude the possibility that other structural elements are included between the substrate and the first electrode or between the first electrode and the piezoelectric layer.

[0025] First Implementation Method

[0026] Piezoelectric element application devices

[0027] First, an example of a liquid jetting device having a recording head, which is an example of a piezoelectric element application device according to the first embodiment of the present invention, namely an inkjet recording device, will be described with reference to the accompanying drawings. Figure 1A perspective view showing the general structure of an inkjet recording device.

[0028] like Figure 1 As shown, in the inkjet recording device (recording device) I, the inkjet recording head unit (head unit) II is detachably mounted on cartridges 2A and 2B. Cartridges 2A and 2B constitute the ink supply unit. The head unit II has multiple inkjet recording heads (recording heads) 1 as described later (see reference). Figure 2 (etc.), and is mounted on a carriage 3. The carriage 3 is mounted on a carriage shaft 5 that is movable relative to the axial direction, and the carriage shaft 5 is mounted on the device body 4. These head units II and carriage 3 are configured, for example, to be able to spray out black ink compositions and colored ink compositions respectively.

[0029] Furthermore, the driving force of the drive motor 6 is transmitted to the carriage 3 via multiple gears (not shown) and a timing belt 7, causing the carriage 3, which houses the head unit II, to move along the carriage shaft 5. On the other hand, a transport roller 8, serving as a transport unit, is provided on the main body 4, through which a recording sheet S, such as paper, is transported. Additionally, the transport unit for transporting the recording sheet S is not limited to a transport roller; it can also be a belt or a drum.

[0030] In the recording head 1, a piezoelectric element 300, which will be described in detail later, is used as a piezoelectric actuator device (see reference 1). Figure 2 By using the piezoelectric element 300, it is possible to avoid the degradation of various characteristics (durability and ink ejection characteristics, etc.) in the recording device I.

[0031] Next, the recording head 1, which is an example of a liquid injection head mounted on a liquid injection device, will be described with reference to the accompanying drawings. Figure 2 An exploded perspective view showing the general structure of an inkjet recorder head. Figure 3 A top view showing the general structure of an inkjet recording head. Figure 4 for Figure 3 A sectional view along line AA′. Additionally, in Figures 2 to 4 The diagram shows a portion of the structure of record header 1, which has been appropriately omitted.

[0032] As shown in the attached figure, the flow channel forming substrate (substrate) 10 comprises silicon (Si). For example, the substrate 10 is made of a single-crystal silicon (Si) substrate.

[0033] On the substrate 10, pressure generating chambers 12 are formed, which are divided by a plurality of partitions 11. The pressure generating chambers 12 are arranged along a direction (+X direction) in which a plurality of nozzle openings 21 that spray ink of the same color are commonly provided.

[0034] An ink supply channel 13 and a connecting channel 14 are formed on one end side (+Y direction side) of the pressure generating chamber 12 in the substrate 10. The ink supply channel 13 is configured such that the opening area on one end side of the pressure generating chamber 12 is reduced. Furthermore, the connecting channel 14 has a width approximately the same as that of the pressure generating chamber 12 in the +X direction. A connecting portion 15 is formed on the outer side (+Y direction side) of the connecting channel 14. The connecting portion 15 forms part of the manifold 100. The manifold 100 becomes a shared ink chamber for each pressure generating chamber 12. Thus, a liquid flow channel consisting of the pressure generating chamber 12, the ink supply channel 13, the connecting channel 14, and the connecting portion 15 is formed on the substrate 10.

[0035] A nozzle plate 20, for example made of SUS, is bonded to another side (the side in the -Z direction). Nozzle openings 21 are arranged along the +X direction on the nozzle plate 20. The nozzle openings 21 communicate with each pressure generating chamber 12. The nozzle plate 20 can be bonded to the substrate 10 by means of adhesive or thermal welding film, etc.

[0036] A vibrating plate 50 is formed on another side (the side in the +Z direction) of the substrate 10. The vibrating plate 50 is, for example, composed of an elastic film 51 formed on the substrate 10 and an insulating film (first diffusion suppression layer) 52 formed on the elastic film 51. The elastic film 51 is, for example, made of silicon dioxide (SiO2), and the first diffusion suppression layer 52 is, for example, made of zirconium oxide (ZrO2).

[0037] Alternatively, the elastic film 51 may not be a component different from the substrate 10. A portion of the surface layer (including the surface) on the +Z direction side of the substrate 10 may be processed thinner and used as the elastic film 51. In this specification, one or both of the substrate 10 and the elastic film 51 are sometimes referred to as a "silicon-containing substrate." Although described later... Figure 5 The image shows an example in which an elastic film 51 and a first diffusion inhibition layer 52 are stacked on the surface of the other side (the side in the +Z direction) of the substrate 10, but the substrate 10 and the elastic film 51 can also be integrated.

[0038] A first electrode 60, a piezoelectric layer 70, and a second electrode 80 are sequentially formed on a first diffusion suppression layer 52 and a silicon-containing substrate (substrate 10 and / or elastic film 51), separated by an adhesion layer. The first electrode 60 may also be formed separated by an adhesion layer (not shown). In this case, the adhesion layer is made of, for example, titanium oxide (TiO₂). X It is composed of materials such as titanium (Ti) and SiN, and has the function of improving the adhesion between the piezoelectric layer 70 and the vibrating plate 50. Alternatively, the adhesion layer can be omitted.

[0039] Although the piezoelectric layer 70 is composed of a so-called KKK-based material containing potassium, sodium, and niobium, these alkali metals sometimes diffuse into the first electrode 60 during the formation of the piezoelectric layer 70. Therefore, by providing a first diffusion suppression layer 52 between the first electrode 60 and the substrate 10, and by having the first diffusion suppression layer 52 function as a termination layer, the arrival of the alkali metals constituting the piezoelectric layer 70 into the substrate 10 can be suppressed. Details of the piezoelectric layer 70 and the first diffusion suppression layer 52 will be described later.

[0040] The first electrode 60 is provided for each pressure generating chamber 12. That is, the first electrode 60 is configured as a separate electrode independent for each pressure generating chamber 12. The first electrode 60 is formed to be smaller than the width of the pressure generating chamber 12 in the ±X direction. Furthermore, the first electrode 60 is formed to be wider than the width of the pressure generating chamber 12 in the ±Y direction. That is, in the ±Y direction, both ends of the first electrode 60 are formed to extend outward beyond the area on the vibrating plate 50 opposite to the pressure generating chamber 12. A lead electrode 90 is connected to one end of the first electrode 60 (the side opposite to the communication channel 14).

[0041] Alternatively, although not provided in this embodiment, a seed layer (also called an orientation control layer) may be provided between the first electrode 60 and the piezoelectric layer 70. In the case of a bonding layer, the seed layer may also be provided on that bonding layer. The seed layer has the function of controlling the orientation of the crystal of the piezoelectric material constituting the piezoelectric layer 70. That is, by providing a seed layer, the crystal of the piezoelectric material constituting the piezoelectric layer 70 can be preferentially oriented towards a predetermined planar orientation.

[0042] A piezoelectric layer 70 is disposed between the first electrode 60 and the second electrode 80. The piezoelectric layer 70 is a thin-film piezoelectric material. The piezoelectric layer 70 is formed with a width wider than that of the first electrode 60 in the ±X direction. Furthermore, the piezoelectric layer 70 is formed with a width wider than that of the pressure generating chamber 12 in the ±Y direction in the ±Y direction. The end of the piezoelectric layer 70 on the ink supply channel 13 side (+Y direction side) is formed to extend further outward than the end of the first electrode 60 on the +Y direction side. That is, the end of the first electrode 60 on the +Y direction side is covered by the piezoelectric layer 70. On the other hand, the end of the piezoelectric layer 70 on the lead electrode 90 side (-Y direction side) is located further inward (+Y direction side) than the end of the first electrode 60 on the -Y direction side. That is, the end of the first electrode 60 on the -Y direction side is not covered by the piezoelectric layer 70.

[0043] The second electrode 80 is continuously disposed across the piezoelectric layer 70 and the vibrating plate 50, spanning the +X direction. In other words, the second electrode 80 is configured as a common electrode shared by multiple piezoelectric layers 70. Although in this embodiment the first electrode 60 is a separate electrode independently disposed corresponding to the pressure generating chamber 12, and the second electrode 80 is a common electrode continuously disposed across the arrangement direction of the pressure generating chamber 12, it is also possible to have the first electrode 60 as a common electrode and the second electrode 80 as a separate electrode.

[0044] In this embodiment, the vibrating plate 50 and the first electrode 60 are displaced by the displacement of the piezoelectric layer 70, which has electromechanical conversion characteristics. That is, the vibrating plate 50 and the first electrode 60 substantially function as vibrating plates. However, in reality, since the second electrode 80 is also displaced by the displacement of the piezoelectric layer 70, the area where the vibrating plate 50, the first electrode 60, the piezoelectric layer 70, and the second electrode 80 are sequentially stacked functions as a movable part (also called a vibrating part) of the piezoelectric element 300.

[0045] A protective substrate 30 is bonded to the substrate 10 (vibrating plate 50) on which the piezoelectric element 300 is formed by an adhesive 35. The protective substrate 30 has a manifold portion 32. At least a portion of the manifold 100 is formed by the manifold portion 32. In this embodiment, the manifold portion 32 extends through the protective substrate 30 in the thickness direction (Z direction) and spans across the width direction (+X direction) of the pressure generating chamber 12. Furthermore, the manifold portion 32 communicates with the communication portion 15 of the substrate 10. With these structures, a manifold 100 is formed that serves as a common ink chamber for each pressure generating chamber 12.

[0046] A piezoelectric element holding portion 31 is formed on the protective substrate 30 in the region containing the piezoelectric element 300. The piezoelectric element holding portion 31 has a space that does not impede the movement of the piezoelectric element 300. This space may or may not be sealed. A through hole 33 is provided on the protective substrate 30, penetrating the protective substrate 30 in the thickness direction (Z direction). The end of the lead electrode 90 is exposed in the through hole 33.

[0047] While materials such as Si, SOI, glass, ceramic materials, metals, and resins can be used as the protective substrate 30, it is more preferable to form it from a material with a thermal expansion coefficient that is approximately the same as that of the substrate 10.

[0048] A drive circuit 120, which functions as a signal processing unit, is fixed on the protective substrate 30. The drive circuit 120 can be, for example, a circuit board or a semiconductor integrated circuit (IC). The drive circuit 120 and the lead electrodes 90 are electrically connected via a connection wiring 121 formed by conductive leads such as bonding leads that penetrate through the through-holes 33. The drive circuit 120 can be connected to the printer controller 200 (see reference 200). Figure 1 Electrical connection. This drive circuit 120 functions as the control unit of the piezoelectric actuator device (piezoelectric element 300).

[0049] Furthermore, a malleable substrate 40, consisting of a sealing film 41 and a fixing plate 42, is bonded to the protective substrate 30. The sealing film 41 is made of a material with low rigidity, while the fixing plate 42 can be made of a hard material such as metal. The area of ​​the fixing plate 42 opposite to the manifold 100 becomes an opening 43 that is completely removed in the thickness direction (Z direction). One side of the manifold 100 (the side on the +Z direction side) is sealed solely by the flexible sealing film 41.

[0050] The recording head 1 then ejects ink droplets in the following manner.

[0051] First, ink is drawn in through an ink inlet connected to an external ink supply unit (not shown), and the manifold 100 is filled with ink up to the nozzle opening 21. Then, a voltage is applied between the first electrode 60 and the second electrode 80 corresponding to the pressure generating chamber 12 according to a recording signal from the drive circuit 120, causing the piezoelectric element 300 to flex. This increases the pressure within each pressure generating chamber 12, causing ink droplets to be ejected from the nozzle opening 21.

[0052] piezoelectric elements

[0053] Next, the structure of the piezoelectric element 300 used as a piezoelectric actuator device for the recording head 1 will be described with reference to the accompanying drawings.

[0054] Figure 5 for Figure 4 An enlarged cross-sectional view along the BB' line. As shown in the attached figure, the piezoelectric element 300 includes: a substrate (substrate 10 and elastic film 51) comprising silicon; a first electrode 60 formed on the silicon-containing substrate; a piezoelectric layer 70 formed on the first electrode 60 and comprising potassium, sodium and niobium; and a second electrode 80 formed on the piezoelectric layer 70.

[0055] Pressure generating chambers 12, divided by multiple partitions 11, are provided on the substrate 10. This structure forms the movable portion of the piezoelectric element 300. The thickness of the first electrode 60 is approximately 50 nm to 300 nm. The piezoelectric layer 70 is a thin film piezoelectric material with a thickness of 50 nm or more and 2000 nm or less. The thickness of the second electrode 80 is approximately 10 nm to 500 nm. The thicknesses of the elements listed herein are examples and can be varied without departing from the spirit of the invention.

[0056] The materials of the first electrode 60 and the second electrode 80 are preferably noble metals such as platinum (Pt) and iridium (Ir) or their oxides. The materials of the first electrode 60 and the second electrode 80 only need to be conductive. The materials of the first electrode 60 and the second electrode 80 can be the same or different.

[0057] A first diffusion suppression layer 52 is disposed between the substrate 10 and the piezoelectric layer 70 in the Z direction. The first diffusion suppression layer 52 comprises an insulating material. The first diffusion suppression layer 52 is preferably an insulating material containing, for example, zirconium. By using a zirconium-containing material as the first diffusion suppression layer 52, it is possible to further suppress the diffusion of alkali metals contained in the piezoelectric material toward the substrate 10 side. From this viewpoint, the first diffusion suppression layer 52 is more preferably composed of zirconium oxide (ZrO2). It may also be composed solely of zirconium oxide (ZrO2).

[0058] As described later, in this embodiment, a portion of the elastic film 51 is exposed in the region between the first electrode 60 arranged along the X direction and the first diffusion suppression layer 52. That is, a plurality of first diffusion suppression layers 52 are disposed along the X direction with respect to the exposed elastic film 51. In addition, since the first diffusion suppression layer 52 disposed under the first electrode 60 within the plurality of first diffusion suppression layers 52 is not concerned with the diffusion of elements from the piezoelectric layer 70, it can also be omitted.

[0059] Previously, cracks sometimes occurred at the interface between the ZrO2 film (which serves as a diffusion-inhibiting layer), the first electrode 60, and the piezoelectric layer 70. Specifically, cracks extended from both ends of the first electrode 60 in the X direction towards the +Z direction. This is believed to be because the contact interface of the piezoelectric layer 70 has two interfaces: one with the ZrO2 film and the other with the first electrode 60, resulting in differences in stress at each interface. In particular, since ZrO2 has a strong effect on inhibiting element diffusion, the change in physical properties at the interface between the KNN-based piezoelectric layer 70 and the ZrO2 film becomes drastic. In other words, when a KNN-based material is used as the piezoelectric layer 70, the region containing the interface between the ZrO2 film, the first electrode 60, and the piezoelectric layer 70 becomes very brittle, thus exhibiting lower resistance to external pressures such as vibration compared to other regions.

[0060] Therefore, in the piezoelectric element 300 of this embodiment, from the viewpoint of the change in physical properties of the contact interface of the piezoelectric layer 70, it is designed to reduce the difference in thermal expansion coefficients at the contact interface.

[0061] Specifically, such as Figure 5 As shown, the surface 60a of the first electrode 60 is defined as the first region A1, the surface 52a of the first diffusion suppression layer 52 is defined as the second region A2, and the silicon-containing substrate between the adjacent first region A1 and second region A2 in the X direction (in) Figure 5 In the case where the surface 51a of the elastic membrane 51 is defined as the third region A3, the piezoelectric layer 70 is continuously disposed on the first region A1, the second region A2, and the third region A3. That is, when viewed from above in the Z direction, a portion of the elastic membrane 51 is exposed in the region between the first electrode 60 and the first diffusion suppression layer 52, and the end 60b of the first electrode 60 is disposed on the exposed elastic membrane 51.

[0062] The interface where the end 60b of the first electrode 60 meets the piezoelectric layer 70 is an interface where stress is easily concentrated. Therefore, by providing a silicon-containing substrate (elastic film 51) below this interface, the difference in the coefficients of thermal expansion between the silicon-containing substrate (elastic film 51) and the piezoelectric layer 70 can be reduced, thereby suppressing the generation of cracks.

[0063] The mechanism by which crack formation can be suppressed can be speculated as follows.

[0064] First, from the viewpoint of mitigating the difference in thermal expansion coefficients, the inventors studied the preferred material for the substrate constituting the interface of the piezoelectric layer 70 using KNN-based materials.

[0065] Figure 8 as well as Figure 9 The figure shows the results of analyzing the elemental distribution of the piezoelectric layer and substrate in the embodiments described below using SIMS (Secondary Ion Mass Spectrometry). Figure 8 The analysis results for Example 1, which used a SiO2 substrate, are as follows. Figure 9 The analytical results for Comparative Example 1, which used a ZrO2 substrate (ZrO2 film), are shown. Additionally, Figure 8 , Figure 9 The results were obtained from the analysis performed from the piezoelectric layer toward the substrate, and the analysis results were shown as the analysis time (horizontal axis) progressed toward the substrate side.

[0066] In Example 1, which uses a SiO2 substrate, as follows: Figure 8 As shown, even after passing the interface with the piezoelectric layer (the definition of "interface" will be described later), the concentrations of potassium (K) and sodium (Na) constituting the piezoelectric do not decrease sharply, but rather show a slow decreasing trend. Therefore, it can be concluded that, when using a SiO2 substrate, the constituent elements of the piezoelectric diffuse towards the SiO2 substrate side.

[0067] When such element diffusion occurs, it is accompanied by the formation of compounds on the substrate (especially the surface layer) or changes in the physical properties near the interface. As a result, it is presumed that the difference in the coefficients of thermal expansion between the piezoelectric layer and the SiO2 substrate is mitigated. Furthermore, a preferred manufacturing method for diffusing the constituent elements of the piezoelectric material towards the SiO2 substrate side will be described later.

[0068] On the other hand, in the comparative example using a ZrO2 substrate, such as Figure 9 As shown, the concentrations of potassium (K) and sodium (Na) constituting the piezoelectric layer decrease sharply when crossing the interface. This suggests that, when using a ZrO2 substrate, the constituent elements of the piezoelectric do not diffuse towards the substrate side (or diffuse very little). Without elemental diffusion, the formation of compounds or changes in properties near the interface, as described above, cannot occur, thus the difference in thermal expansion coefficients is not mitigated.

[0069] Based on the above analysis, it can be concluded that the substrate (in the piezoelectric layer) forms the interface with the piezoelectric layer. Figure 5 The material of the substrate 10 or the elastic film 51 is preferably SiO2. Moreover, by using a SiO2 substrate as the substrate, the difference in the coefficients of thermal expansion between the piezoelectric layer and the SiO2 substrate is mitigated by the diffusion of elements, which results in the suppression of crack formation near the interface.

[0070] Here, the "interface between the piezoelectric layer and the substrate" as used in this embodiment is defined as follows.

[0071] First, such as Figure 8 , 9 As shown, in the SIMS analysis results, the flat peak intensity of the substrate's constituent elements (e.g., silicon (Si)) is averaged (arrow P), and the portion intersecting with half of this intensity is defined as interface 1 between the piezoelectric layer and the substrate. Next, the point where the intensity begins to decrease from the flat peak intensity of the substrate's constituent elements (e.g., silicon (Si)) is defined as interface 2. In this embodiment, the region between interface 1 and interface 2 is defined as the "interface between the piezoelectric layer and the substrate".

[0072] Although interfaces are generally defined by a specific surface, accurately determining the interface between the piezoelectric layer and the substrate is very difficult in analyses performed by SIMS. Therefore, it is assumed that the "interface between the piezoelectric layer and the substrate" in this embodiment has a certain width, and the area between interface 1 and interface 2 is defined as the "interface between the piezoelectric layer and the substrate".

[0073] Furthermore, the presence or absence of diffusion at the interface of the elements constituting the piezoelectric material is determined according to the following criteria.

[0074] First, such as Figure 8 , 9 As shown, the average peak intensities of sodium (Na) and potassium (K) were calculated from the start of the analysis performed by SIMS (analysis time: 0 seconds) up to interface 1 (arrow Q). Na and the arrow mark Q K The intensity that drops two digits from the average is considered the location where the element disappears, that is, the part where diffusion did not occur (arrow mark R). Na and the arrow mark R K ).

[0075] When such a definition and Figure 8 In comparison, in Example 1, it was observed that sodium (Na) and potassium (K) diffused across the interface into the interior of the SiO2 substrate.

[0076] On the other hand, in comparative examples, such as Figure 9 As shown, sodium (Na) and potassium (K) disappear at the interface and do not diffuse toward the substrate.

[0077] From the perspective of the above mechanism, it is preferable that the silicon-containing substrate in this embodiment (in) Figure 5 In the case of elastic film 51), SiO2 is contained. More preferably, the substrate containing silicon is a substrate made of SiO2.

[0078] Furthermore, cracks can occur near the interface with the piezoelectric layer 70. Therefore, it is sufficient that the silicon-containing substrate is provided at least in the third region A3. In other words, regions other than the interface where stress is easily concentrated, such as the interface between the end 60b of the first electrode 60 and the piezoelectric layer 70, may not be formed by a silicon-containing substrate. In addition, the second electrode 80 is more significantly affected by crack formation. Therefore, in the region corresponding to the arrangement area of ​​the second electrode 80 (the region overlapping with the second electrode 80 in the Z direction), it is sufficient that only a portion of the silicon-containing substrate is exposed, and when viewed from above in the Z direction, the silicon-containing substrate may not need to span the entire circumference of the piezoelectric layer 70.

[0079] As described above, the piezoelectric layer 70 involved in this embodiment is a piezoelectric layer composed of a thin film, and is formed by a solution method (also known as a liquid phase method or wet method) such as the MOD method or the sol-gel method, or a gas phase method such as the sputtering method. In this embodiment, it is a perovskite-type composite oxide containing potassium (K), sodium (Na), and niobium (Nb) formed by a solution method. That is, the piezoelectric layer 70 contains a piezoelectric material composed of a KNN-based composite oxide represented by the following formula (1).

[0080] (K X Na 1-X NbO3···(1)

[0081] (0.1≤X≤0.9)

[0082] The piezoelectric material constituting the piezoelectric layer 70 can be any KNN-based composite oxide and is not limited to the composition represented by the above formula (1). For example, other metallic elements (additives) may be included at points A and B of the potassium sodium niobate. Examples of such additives include manganese (Mn), lithium (Li), barium (Ba), calcium (Ca), strontium (Sr), zirconium (Zr), titanium (Ti), bismuth (Bi), tantalum (Ta), antimony (Sb), iron (Fe), cobalt (Co), silver (Ag), magnesium (Mg), zinc (Zn), and copper (Cu).

[0083] Such additives may include more than one. Generally, the amount of additive is 20% or less, preferably 15% or less, and more preferably 10% or less, relative to the total amount of the elements that are the main components. Although various properties can be enhanced by using additives, thereby facilitating the diversification of structure and function, from the viewpoint of maximizing the properties derived from KNN, it is preferable that KNN is present in more than 80%. Furthermore, even in the case of a composite oxide containing these other elements, it is preferable that it is configured to have an ABO3-type perovskite structure.

[0084] Furthermore, in this specification, "perovskite-type composite oxides containing K, Na, and Nb" refers to "composite oxides with an ABO3-type perovskite structure containing K, Na, and Nb," and is not limited to composite oxides with an ABO3-type perovskite structure containing K, Na, and Nb. That is, in this specification, "perovskite-type composite oxides containing K, Na, and Nb" includes piezoelectric materials represented as mixed crystals, which include composite oxides with an ABO3-type perovskite structure containing K, Na, and Nb (e.g., the KNN-based composite oxides illustrated above), and other composite oxides having an ABO3-type perovskite structure.

[0085] While other composite oxides are not limited to the scope of this embodiment, lead-free (Pb) piezoelectric materials are preferred. Furthermore, lead-free (Pb) and bismuth (Bi)-free piezoelectric materials are more preferably other composite oxides. Accordingly, a piezoelectric element 300 with excellent biocompatibility and low environmental impact is achieved.

[0086] According to the piezoelectric element 300 described in Embodiment 1 above, a silicon-containing substrate is disposed below the interface where the end 60b of the first electrode 60 meets the piezoelectric layer 70. This allows the constituent elements of the piezoelectric material to diffuse towards the SiO2 substrate at the interface between the silicon-containing substrate and the piezoelectric layer 70. When element diffusion occurs, it causes the formation of compounds or changes in the physical properties near the interface. As a result, the difference in the coefficients of thermal expansion between the silicon-containing substrate and the piezoelectric layer 70 decreases, thereby suppressing crack formation.

[0087] Furthermore, although an inkjet recording head has been described as an example of a liquid ejector head in the above embodiments, the present invention can be applied to liquid ejector heads in general, as well as to liquid ejector heads that eject liquids other than ink. Other examples of liquid ejector heads include various recording heads used in image recording devices such as printers, color material ejector heads used in the manufacture of color filters such as liquid crystal displays, electrode material ejector heads used in the electrode formation of organic EL displays, FED (field emission display), and biological organic matter ejector heads used in the manufacture of biochips.

[0088] Furthermore, the present invention is not limited to piezoelectric elements mounted within liquid jet heads, but can also be applied to piezoelectric elements mounted within other piezoelectric element application devices. Examples of piezoelectric element application devices include ultrasonic devices, motors, pressure sensors, pyroelectric elements, and strongly magnetic elements. In addition, complete systems utilizing these piezoelectric element application devices, such as liquid jetting devices utilizing the aforementioned liquid jet heads, ultrasonic sensors utilizing the aforementioned ultrasonic devices, automatic devices utilizing the aforementioned motors as drive sources, IR sensors utilizing the aforementioned pyroelectric elements, and strongly magnetic memory utilizing strongly magnetic elements, are also included in piezoelectric element application devices.

[0089] Variation Example 1

[0090] Next, the piezoelectric element 300A, which is a variation of the first embodiment, will be described with reference to the accompanying drawings. In the following description, structures that have the same or similar functions as those in the first embodiment will be marked with the same symbols. Furthermore, repeated descriptions of these structures will sometimes be omitted.

[0091] Figure 6 for Figure 4 An enlarged cross-sectional view along line BB'. As shown in the attached figure, in this modified example, a first diffusion suppression layer 152 is also disposed between the silicon-containing substrate (substrate 10 and elastic film 51) and the first electrode 60. The first diffusion suppression layer 152 may also be disposed on the surface of the silicon-containing substrate.

[0092] Furthermore, in this modified example, the first electrode 60 is continuously formed on the fourth region A4 and the fifth region A5, wherein the fourth region A4 is the surface 152a of the first diffusion suppression layer 152, and the fifth region A5 is the surface 51a of the substrate. The fifth region A5 includes the end portion 152b of the first electrode 60. That is, the surface 152a and the end portion 152b of the first diffusion suppression layer 152 are covered by the first electrode 60. When the end portion 152b of the first diffusion suppression layer 152 is exposed from the end portion 60b of the first electrode 60 toward the piezoelectric layer 70, the exposed portion may become the cause of cracks.

[0093] According to the piezoelectric element 300A with the structure of Modified Example 1 described above, a first diffusion suppression layer 152 is also disposed between the first electrode 60 and the silicon-containing substrate (substrate 10 and elastic film 51). This further suppresses the diffusion of alkali metal contained in the piezoelectric layer 70 towards the substrate side.

[0094] Variation Example 2

[0095] Next, the piezoelectric element 300B, which is a variation of the first embodiment, will be described with reference to the accompanying drawings. In the following description, structures having the same or similar functions as those in the first embodiment will be marked with the same symbols. Furthermore, repeated descriptions of these structures will sometimes be omitted.

[0096] Figure 7 for Figure 4 The figure shows an enlarged cross-sectional view along line BB′. As shown in the figure, in this modified example, a second diffusion suppression layer 57 is disposed between the first electrode 60 and the piezoelectric layer 70 in the Z direction. The second diffusion suppression layer 57 is made of an insulating material. Preferably, the second diffusion suppression layer 57 is a conductive material containing iridium (Ir), for example. By using a material containing iridium as the second diffusion suppression layer 57, it is possible to further suppress the diffusion of alkali metal contained in the piezoelectric material towards the first electrode 60 and the substrate 10. From this point of view, it is more preferable that the second diffusion suppression layer 57 contains iridium oxide (IrO2). It may also be composed solely of iridium oxide (IrO2).

[0097] Next, an example of a method for manufacturing the piezoelectric element 300 will be described.

[0098] First, a silicon-containing substrate (hereinafter also referred to as a "wafer") is prepared, and an elastic film 51 made of silicon dioxide is formed on its surface by thermal oxidation of the substrate.

[0099] Next, in the region outside the formation area of ​​the first diffusion inhibition layer 52 on the elastic film 51, a resist of a predetermined shape is formed as a mask, and the elastic film 51 is patterned. Then, in the patterned region, a zirconium film is formed by sputtering, and the first diffusion inhibition layer 52 is formed by thermal oxidation of the zirconium film.

[0100] Next, a first electrode 60 is formed on the elastic film 51 and the first diffusion inhibition layer 52 by a common method (sputtering or vapor deposition, etc.), and a pattern is formed thereon. The first electrode 60 may also be formed with a bonding layer (e.g., titanium oxide) in between.

[0101] Next, a multilayer piezoelectric film is formed by overlapping the first electrode 60, the elastic film 51, and the first diffusion suppression layer 52.

[0102] The piezoelectric layer 70 is formed by these multilayered piezoelectric films. Furthermore, the piezoelectric layer 70 can be formed using solution methods (chemical solution methods), such as MOD method or sol-gel method. Thus, by using solution methods to form the piezoelectric layer 70, the productivity of the piezoelectric layer 70 can be improved. In this way, the piezoelectric layer 70 formed using solution methods is formed by repeatedly performing a series of steps from the process of applying the precursor solution (coating process) to the process of firing the precursor film (firing process).

[0103] The specific steps for forming the piezoelectric layer 70 using a solution method are as follows.

[0104] First, the precursor solution containing the predetermined metal complex is prepared. The precursor solution is a liquid formed by dissolving or dispersing a metal complex containing K, Na, and Nb, which can be formed by calcination, in an organic solvent. At this time, the metal complex containing additives such as Mn may also be further mixed.

[0105] Examples of metal complexes containing potassium (K) include potassium 2-ethylhexanoate and potassium acetate. Examples of metal complexes containing sodium (Na) include sodium 2-ethylhexanoate and sodium acetate. Examples of metal complexes containing niobium (Nb) include niobium 2-ethylhexanoate and niobium pentaethoxy. When Mn is added as an additive, examples of metal complexes containing Mn include manganese 2-ethylhexanoate. In this case, two or more metal complexes can also be used together. For example, potassium 2-ethylhexanoate and potassium acetate can be used together as metal complexes containing potassium (K). Examples of solvents include 2-n-butoxyethanol or n-octane or mixtures thereof. The precursor solution may also contain additives that stabilize the dispersion of metal complexes containing K, Na, and Nb. Examples of such additives include 2-ethylhexanoic acid.

[0106] Then, the precursor solution described above is coated onto the substrate 10 on which the elastic film 51, the first diffusion inhibition layer 52 and the first electrode 60 are formed, thereby forming a precursor film (coating process).

[0107] Next, the precursor film is heated to a predetermined temperature, for example, about 130°C to 250°C, and dried for a fixed time (drying process).

[0108] The heating rate in the drying process is preferably set to 30°C to 350°C / sec. By using a solution method and firing the piezoelectric film at such a heating rate, a piezoelectric layer 70 that is not a pseudo-cubic crystal can be achieved. Furthermore, the "heating rate" mentioned here refers to the rate of temperature change over time from 350°C until the target firing temperature is reached.

[0109] Next, the dried precursor film is heated to a predetermined temperature, such as 250°C to 500°C, and held at that temperature for a fixed time to perform degreasing (degreasing process).

[0110] Heating devices used in the drying, degreasing, and firing processes include, for example, RTA (Rapid Thermal Annealing) devices or heating plates that use infrared lamps for heating. These processes are repeated multiple times to form a piezoelectric layer 70 composed of multiple piezoelectric films. Alternatively, in a series of processes from the coating process to the firing process, the firing process can be performed after the processes from the coating process to the degreasing process have been repeated multiple times.

[0111] Furthermore, before and after forming the second electrode 80 on the piezoelectric layer 70, a reheating treatment (post-annealing) can be performed in the temperature range of 600°C to 800°C as needed. By performing post-annealing in this manner, a good interface between the piezoelectric layer 70 and the first electrode, as well as a good interface between the piezoelectric layer 70 and the second electrode 80, can be formed, and the crystallinity of the piezoelectric layer 70 can be improved.

[0112] After the firing process, the piezoelectric layer 70, composed of multiple piezoelectric films, is formed into an image. Figure 5 The shape shown. Image formation can be performed through dry etching such as reactive ion etching, ion milling, or wet etching using an etchant.

[0113] Next, a second electrode 80 is formed on the piezoelectric layer 70. The second electrode 80 can be formed using the same method as the first electrode 60.

[0114] Through the above processes, a piezoelectric element 300 having a first electrode 60, a piezoelectric layer 70, and a second electrode 80 is manufactured.

[0115] Example

[0116] The present invention will now be described in more detail by way of examples, but the present invention is not limited to these examples in any way.

[0117] Example 1

[0118] First, an elastic film 51 made of silicon dioxide is formed on the substrate by thermal oxidation of the surface of the silicon substrate (6 inches) that serves as the substrate, thereby obtaining the substrate substrate.

[0119] Next, a piezoelectric layer 70 is formed on the substrate using the following steps.

[0120] First, a precursor solution consisting of potassium 2-ethylhexanoate, sodium 2-ethylhexanoate, lithium 2-ethylhexanoate, niobium 2-ethylhexanoate, and manganese 2-ethylhexanoate is applied to the substrate by spin coating to form a precursor film (coating process).

[0121] Afterward, the precursor membrane was dried at 180°C (drying process), and then degreased at 380°C for 3 minutes (degreasing process).

[0122] Next, the degreased precursor film was subjected to RTA (Rapid Themal Annealing) at 700°C for 3 minutes to form a piezoelectric film (firing process). This process from coating to firing was repeated multiple times until cracks were detected, thereby producing a KNN-based piezoelectric layer 70 composed of multiple piezoelectric films.

[0123] Comparative Example 1

[0124] In the fabrication of the aforementioned substrate, a zirconium film is fabricated by sputtering a zirconium film onto a silicon dioxide film (elastic film 51) and then thermally oxidizing it. A piezoelectric layer 70 is then formed on the zirconium oxide film. All other aspects are the same as in Example 1.

[0125] Comparative Example 2

[0126] In the fabrication of the aforementioned substrate, an Al2O3 film was formed on a silicon dioxide film (elastic film 51) using the ALD method. Then, a piezoelectric layer 70 was formed on the Al2O3 film. All other aspects were the same as in Example 1.

[0127] Comparative Example 3

[0128] In the fabrication of the aforementioned substrate, a Ta2O5 film was formed on a silicon dioxide film (elastic film 51) by sputtering. Then, a piezoelectric layer 70 was formed on the Ta2O5 film. All other aspects were the same as in Example 1.

[0129] The following confirmation of element diffusion and crack formation were performed for each of the above embodiments and comparative examples. The results are shown in Table 1.

[0130] Confirmation of element diffusion

[0131] The elemental diffusion was confirmed using a secondary ion mass spectrometry (SIMS) system (“IMS-7f sector type”, manufactured by CAMECA). In the primary ion array, a beam current of 10 nA was applied to a 15 keV Cs+ ion at a 100 μm square, and negative secondary ions were detected from the center at 33 μm φ. An electron gun was used to prevent charging.

[0132] Crack confirmation

[0133] The presence or absence of cracks was determined by dark-field observation using a metal microscope and a 50x objective lens. Table 1 shows the total number of piezoelectric films stacked up to the point of crack formation.

[0134] Table 1

[0135] Example 1 <![CDATA[SiO2]]> 10 floors and above Comparative Example 1 <![CDATA[ZrO2]]> 4 floors Comparative Example 2 <![CDATA[Al2O3]]> 4 floors Comparative Example 3 <![CDATA[Ta2O s ]]> 5 floors

[0136] Test results

[0137] According to the results in Table 1, in Example 1 where SiO2 was used as the substrate material, no cracks occurred even when 10 layers of the piezoelectric film (KNN) were stacked. On the other hand, when ZrO2, Al2O3, and Ta2O5 were used, cracks occurred with fewer than 5 layers.

[0138] Figure 8 The analysis results for Example 1, which used a SiO2 substrate, are as follows. Figure 9 The analysis results are for Comparative Example 1, which uses a ZrO2 substrate (ZrO2 film).

[0139] like Figure 8 As shown, when SiO2 is used as the substrate, it is known that potassium (K) and sodium (Na), which are constituent elements of KNN, are contained within the substrate. In other words, it is known that these constituent elements of KNN diffuse obliquely into the substrate from the interface.

[0140] Therefore, in order to suppress the generation of cracks, it is preferable to use SiO2 as the material disposed at the contact interface with the piezoelectric layer.

[0141] Symbol Explanation

[0142] I…Inkjet recording device (liquid jet device); II…Inkjet recording head unit (head unit); 1…Inkjet recording head (liquid jet head); 10…Substrate; 12…Pressure generating chamber; 13…Ink supply channel; 14…Connecting channel; 15…Connecting part; 20…Nozzle plate; 21…Nozzle opening; 30…Protective substrate; 31…Piezoelectric element holding part; 32…Manifold part; 40…Moldable substrate; 50…Vibrating plate; 51…Elastic membrane; 52…First diffusion suppression layer; 57…Second diffusion suppression layer; 60…First electrode; 70…Piezoelectric layer; 80…Second electrode; 90…Lead electrode; 100…Manifold; 300…Piezoelectric element; A1…First region; A2…Second region; A3…Third region; A4…Fourth region; A5…Fifth region.

Claims

1. A piezoelectric element, characterized in that, have: Substrate, comprising silicon; A first electrode is formed on the substrate; A piezoelectric layer is formed on the first electrode and comprises potassium, sodium and niobium; The second electrode is formed on the piezoelectric layer. A first diffusion suppression layer comprising an insulating material is disposed between the substrate and the piezoelectric layer. The piezoelectric layer is continuously formed on a first region, a second region, and a third region, wherein the first region is the surface of the first electrode, the second region is the surface of the first diffusion suppression layer, and the third region is the surface of the substrate. The third region is configured between the first region and the second region.

2. The piezoelectric element as described in claim 1, characterized in that, The first diffusion inhibition layer contains zirconium.

3. The piezoelectric element as described in claim 1 or 2, characterized in that, A first diffusion suppression layer is disposed between the substrate and the first electrode. The first electrode is continuously formed on the fourth and fifth regions, wherein the fourth region is the surface of the first diffusion suppression layer and the fifth region is the surface of the substrate. The fifth region includes the end of the first electrode.

4. The piezoelectric element as described in claim 1, characterized in that, A second diffusion suppression layer containing iridium is disposed between the first electrode and the piezoelectric layer.

5. A piezoelectric element application device, characterized in that, The piezoelectric element is provided with any one of claims 1 to 4.

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