Piezoelectric element, head chip, liquid ejecting apparatus, and sensor

Abstract

Provided is a piezoelectric element, a head chip, a liquid ejecting apparatus, and a sensor, which can suppress a decrease in efficiency (linearity) of displacement of a vibrating plate. The piezoelectric element of the present application includes a first electrode, a piezoelectric layer formed above the first electrode, and a second electrode formed above the piezoelectric layer, wherein the piezoelectric layer contains potassium, sodium, and niobium, and a Young's modulus of the piezoelectric layer measured by a nanoindentation method exceeds 130 GPa.

Description

TECHNICAL FIELD

[0001] The present application relates to a piezoelectric element, a head chip, a liquid ejecting apparatus, and a sensor. BACKGROUND

[0002] A piezoelectric element generally has a substrate, a piezoelectric layer having an electromechanical conversion characteristic, and two electrodes sandwiching the piezoelectric layer. In recent years, development of devices using such a piezoelectric element as a driving source (piezoelectric element application device) is in vogue. As one of the piezoelectric element application devices, there are a liquid ejecting head typified by an inkjet recording head, a MEMS element typified by a piezoelectric MEMS element, an ultrasonic measuring apparatus typified by an ultrasonic sensor, and a piezoelectric actuator device.

[0003] As one example of a piezoelectric element, for example, a piezoelectric element containing lead, zirconium, and titanium and having a piezoelectric layer (PZT layer) with a Young's modulus of 75 GPa and a first electrode (platinum layer) with a Young's modulus of 200 GPa is disclosed in Patent Literature 1.

[0004] Here, in recent years, from the viewpoint of reducing environmental load, development of a non-lead piezoelectric material in which the content of lead (Pb) is suppressed is being promoted. As a main material of a piezoelectric element in which the content of lead is low, for example, potassium sodium niobate (KNN; (K, Na)NbO3) is proposed.

[0005] However, as described in Patent Literature 1, in a case where a top electrode with a larger Young's modulus is provided on a piezoelectric layer with a smaller Young's modulus, there is a problem that the piezoelectric layer is deformed by stress received from the top electrode, and in conjunction therewith, flexure of the vibration plate to the pressure chamber side (initial flexure) occurs.

[0006] Further, there is a problem that the piezoelectric layer with a smaller Young's modulus cannot sufficiently bend the vibration plate at the time of driving of the piezoelectric element, and thus the displacement amount decreases (linearity deteriorates) particularly at the time of high voltage driving.

[0007] In a case of a piezoelectric layer with a smaller Young's modulus and relatively soft, the variation at the time of driving of the piezoelectric element cannot be sufficiently transmitted to the vibration plate, and thus a part of the driving is consumed by deformation of the piezoelectric layer itself. Therefore, particularly at the time of high voltage, there is a problem that the larger the variation, the larger the ratio of the driving force consumed by the deformation of the piezoelectric layer itself, and thus the efficiency of the variation of the vibration plate decreases.

[0008] Further, the piezoelectric layer that is comparatively soft sometimes deforms due to stress of the upper electrode (second electrode) from the stage of film formation, and as a result, there is a problem in that initial deflection of the vibration plate becomes large. When deflection of the vibration plate to the pressure chamber side occurs, the volume of the pressure chamber decreases, and thus, for example, a decrease in the amount of liquid droplet ejection can be caused.

[0009] According to such circumstances, there is a demand for a piezoelectric element that can suppress a decrease in efficiency (linearity) of displacement of a vibration plate even when driven at a high voltage (for example, 20 to 50 V).

[0010] In addition, such a problem is not limited to a piezoelectric element used in a piezoelectric actuator mounted on a liquid ejection head typified by an inkjet recording head, but also occurs in a piezoelectric element used in other piezoelectric element application devices.

[0011] Patent Document 1: Japanese Patent Application Publication No. 2012-240366 SUMMARY

[0012] To solve the above-described problems, according to a first aspect of the present application, a piezoelectric element can be provided, the piezoelectric element including: a first electrode; a piezoelectric layer formed above the first electrode; and a second electrode formed above the piezoelectric layer, the piezoelectric layer containing potassium, sodium, and niobium, and a Young's modulus of the piezoelectric layer measured by a nanoindentation method exceeding 130 GPa.

[0013] According to a second aspect of the present application, a head chip can be provided, the head chip including: a nozzle plate including nozzles that eject liquid droplets; a pressure generation chamber that communicates with the nozzles; a flow path forming substrate disposed above the nozzle plate and forming the pressure generation chamber; a vibration plate that forms part of a wall surface of the pressure generation chamber; the piezoelectric element of the first aspect disposed on the vibration plate; and a voltage application unit that applies a voltage to the piezoelectric element.

[0014] According to a third aspect of the present application, a liquid ejection apparatus can be provided, the liquid ejection apparatus including: a conveyance unit that conveys a medium; and a liquid droplet ejection head that applies liquid droplets to the medium, the liquid droplet ejection head including the head chip of the second aspect.

[0015] According to a fourth aspect of the present application, a sensor can be provided, the sensor including: the piezoelectric element of the first aspect; and a voltage detection unit that detects a voltage output from the piezoelectric element. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 A perspective view showing the outline structure of the recording apparatus of Embodiment 1.

[0017] Figure 2 Fig. 1 is a perspective view of a recording head of a recording apparatus according to the present embodiment. Figure 1

[0018] Figure 3 Figure 1

[0019] Figure 4 Figure 1

[0020] Figure 5 Figure 4

[0021] Figure 6A

[0022] Figure 6B DETAILED DESCRIPTION

[0023] Embodiments of the present application will be described below with reference to the accompanying drawings. The following description is given as an illustration of one embodiment of the present application, which can be arbitrarily changed within the scope of the present application. In addition, components to which the same reference numerals are assigned in each drawing represent the same components, and the description is appropriately omitted. The numbers after the letters constituting the reference numerals are referred to by the reference numerals including the same letters, and are used in order to distinguish elements having the same structure from each other. In the case where it is not necessary to distinguish elements indicated by the reference numerals including the same letters from each other, the elements are referred to by the reference numerals including only the letters, respectively.

[0024] In each drawing, X, Y, and Z represent three spatial axes orthogonal to each other. In the present specification, the directions along these axes are set as a first direction X (X direction), a second direction Y (Y direction), and a third direction Z (Z direction), respectively, and the directions indicated by the arrow marks of each drawing are set as positive (+) directions, and the opposite directions of the arrow marks are set as negative (-) directions. The X direction and the Y direction represent in-plane directions of a plate, a layer, and a film, and the Z direction represents a thickness direction or a stacking direction of the plate, the layer, and the film.

[0025] ​​​​​​​​​Moreover, the shapes and sizes of the structural elements, i.e., the individual parts, the plate, the layer, and the film thickness, the relative positional relationship, the repeating unit, and the like, which are illustrated in the respective drawings, are sometimes exaggerated on the basis of the explanation of the present application. In addition, the term "upper" of the present specification is not limited to the case where the positional relationship of the structural elements is "directly above". For example, the expression "a first electrode on a substrate" or "a piezoelectric layer on a first electrode" recited later does not exclude the case where other structural elements are included between the substrate and the first electrode or between the first electrode and the piezoelectric layer.

[0026] Liquid ejecting apparatus

[0027] First, an inkjet recording apparatus, which is one example of a liquid ejecting apparatus according to an embodiment of the present application, will be described with reference to the drawings. Figure 1 A perspective view showing the outline structure of the inkjet recording apparatus.

[0028] As Figure 1 shown, in the inkjet recording apparatus (recording apparatus) I, inkjet recording head units (liquid droplet ejecting heads, head units) II are provided on cartridges 2A, 2B in a detachable manner. The cartridges 2A, 2B constitute ink supply units. The head units II have a plurality of inkjet recording heads (head chips, recording heads) 1 (see Figure 2 and the like) and are mounted on a carriage 3. The carriage 3 is provided on a carriage shaft 5, which is installed on an apparatus main body 4, in a manner that is movable with respect to the axial direction. These head units II and the carriage 3 are constituted, for example, in a manner that enables black ink compositions and color ink compositions to be ejected respectively.

[0029] Further, the driving force of a driving motor 6 is transmitted to the carriage 3 via a plurality of gears and a timing belt 7, which are not shown, to move the carriage 3, on which the head units II are mounted, along the carriage shaft 5. On the other hand, a conveyance roller 8, which is a conveyance unit, is provided on the apparatus main body 4, and a recording sheet S, which is a recording medium (medium), is conveyed by the conveyance roller 8. In addition, the conveyance unit that conveys the recording sheet S is not limited to the conveyance roller, but can be a belt or a roller, or the like.

[0030] In the recording head (head chip) 1, a piezoelectric element 300 (see Figure 2 and the like) recited later is used as a piezoelectric actuator device. By using the piezoelectric element 300, it is possible to avoid the reduction in various characteristics (piezoelectric characteristics, durability, and ink ejection characteristics, and the like) in the recording apparatus I. The liquid ejecting apparatus of the present embodiment is particularly capable of sufficiently suppressing the reduction in piezoelectric characteristics (particularly, the displacement amount) by applying the piezoelectric element 300 recited later.

[0031] Next, a recording head (head chip) 1 as an example of a head chip mounted on a liquid ejection device will be described with reference to the drawings. Figure 2 is an exploded perspective view showing the outline structure of the inkjet recording head. Figure 3 is a plan view showing the outline structure of the inkjet recording head. Figure 4 is Figure 3 is an A-A' line sectional view. In addition, in Figures 2 to 4 , a part of the structure of the recording head 1 is shown, and is appropriately omitted.

[0032] As shown in the drawings, the recording head (head chip) 1 is provided with: a nozzle plate 20 provided with nozzles 21 that eject liquid droplets; pressure generation chambers 12 that communicate with the nozzles 21; a substrate 10 and a partition wall (flow path forming substrate) 11 that are provided on the nozzle plate 20 and form the pressure generation chambers 12; a vibration plate 50 that forms a part of the wall surface of the pressure generation chambers 12; a piezoelectric element 300 that is provided on the vibration plate 50; and a lead electrode (voltage application part) 90 that applies a voltage to the piezoelectric element 300.

[0033] The substrate 10 contains silicon (Si). For example, the substrate 10 is composed of a single-crystal silicon (Si) substrate.

[0034] A plurality of partition walls 11 are formed on the substrate 10. The plurality of pressure generation chambers 12 are divided by the partition walls 11. The pressure generation chambers 12 are arranged in a direction (+X direction) in which a plurality of nozzles 21 that eject the same color of ink are commonly provided.

[0035] On one end portion side (+Y direction side) of the substrate 10, an ink supply passage 13 and a communication passage 14 are formed. The ink supply passage 13 is composed in such a manner that the opening area of the one end portion side of the pressure generation chamber 12 becomes smaller. In addition, the communication passage 14 has substantially the same width as the pressure generation chamber 12 in the +X direction. A communication part 15 is formed on the outside (+Y direction side) of the communication passage 14. The communication part 15 constitutes a part of a manifold 100. The manifold 100 becomes an ink chamber that is common to each of the pressure generation chambers 12. In this way, on the substrate 10, a liquid flow path composed of the pressure generation chamber 12, the ink supply passage 13, the communication passage 14, and the communication part 15 is formed.

[0036] The nozzle plate 20 made of, for example, SUS is joined to one face (-Z direction side face) of the substrate 10. On the nozzle plate 20, the nozzles 21 are arranged in the +X direction. The nozzles 21 communicate with each of the pressure generation chambers 12. The nozzle plate 20 can be joined to the substrate 10 by an adhesive or a heat-welding film or the like.

[0037] A vibration plate 50 is formed on the other face of the substrate 10 (the face on the +Z direction side). The vibration plate 50 is constituted by, for example, an elastic film 51 formed on the substrate 10, and an insulator film 52 formed on the elastic film 51. The elastic film 51 is constituted by, for example, silicon dioxide (SiO2), and the insulator film 52 is constituted by, for example, zirconium oxide (ZrO2). The elastic film 51 can also be a component different from the substrate 10. A portion of the substrate 10 can also be processed to be thin, and used as the elastic film 51. The elastic film 51 is not limited to SiO2, and can also be a film constituted by, for example, aluminum oxide (Al2O3), tantalum (V) oxide (Ta2O5), silicon nitride (SiN), or the like.

[0038] On the insulator film 52, a piezoelectric element 300 including a first electrode 60, a piezoelectric layer 70, and a second electrode 80 is formed with a close contact layer 56 interposed therebetween. The close contact layer 56 is constituted by, for example, titanium oxide (TiOX), titanium (Ti), SiN, or the like, and has a function of improving the close contact property of the piezoelectric layer 70 with the vibration plate 50. The close contact layer 56 can also be omitted.

[0039] Although the piezoelectric layer 70 is constituted by a so-called KKK system material including potassium, sodium, and niobium, these alkali metals sometimes diffuse in the first electrode 60 during the formation of the piezoelectric layer 70. Therefore, by providing the insulator film 52 between the first electrode 60 and the substrate 10, and causing the insulator film 52 to function as a stopper layer, it is possible to suppress the arrival of the alkali metals constituting the piezoelectric layer 70 at the substrate 10.

[0040] The first electrode 60 is provided for each pressure generating chamber 12. That is, the first electrode 60 is constituted as a separate electrode independent for each pressure generating chamber 12. The first electrode 60 is formed to be smaller in width than the pressure generating chamber 12 in the ±X direction. Further, the first electrode 60 is formed to be wider than the pressure generating chamber 12 in the ±Y direction. That is, in the ±Y direction, both end portions of the first electrode 60 are formed to be further outside than the region on the vibration plate 50 facing the pressure generating chamber 12. On the one end portion side of the first electrode 60 (the side opposite to the communication passage 14), a lead electrode (voltage application portion) 90 applying a voltage to the piezoelectric element 300 is connected.

[0041] The piezoelectric layer 70 is provided between the first electrode 60 and the second electrode 80. The piezoelectric layer 70 is a thin-film piezoelectric body. The piezoelectric layer 70 is formed in a width wider than the width of the first electrode 60 in the ±X direction. Further, the piezoelectric layer 70 is formed in a width wider than the length of the pressure generation chamber 12 in the ±Y direction. The end portion of the piezoelectric layer 70 on the ink supply passage 13 side (+Y direction side) is formed to the outside than the end portion of the first electrode 60 on the +Y direction side. That is, the end portion of the first electrode 60 on the +Y direction side is covered by the piezoelectric layer 70. On the other hand, the end portion of the piezoelectric layer 70 on the lead electrode 90 side (-Y direction side) is at the inside (+Y direction side) than the end portion of the first electrode 60 on the -Y direction side. That is, the end portion of the first electrode 60 on the -Y direction side is not covered by the piezoelectric layer 70.

[0042] The second electrode 80 is provided across the +X direction in a continuous manner over the piezoelectric layer 70 and the vibrating plate 50. That is, the second electrode 80 is configured as a common electrode shared by the plurality of piezoelectric layers 70. Although the first electrode 60 is configured as a separate electrode provided independently corresponding to the pressure generation chamber 12 and the second electrode 80 is configured as a common electrode provided continuously across the arrangement direction of the pressure generation chamber 12 in the present embodiment, the first electrode 60 can be configured as a common electrode and the second electrode 80 can be configured as a separate electrode.

[0043] In the present embodiment, the vibrating plate 50 and the first electrode 60 are displaced by the displacement of the piezoelectric layer 70 having the electromechanical conversion characteristics. That is, the vibrating plate 50 and the first electrode 60 substantially have a function as a vibrating plate. However, in fact, since the second electrode 80 is also displaced by the displacement of the piezoelectric layer 70, the region in which the vibrating plate 50, the first electrode 60, the piezoelectric layer 70, and the second electrode 80 are sequentially stacked functions as a movable portion (also referred to as a vibrating portion) of the piezoelectric element 300.

[0044] Further, in the present embodiment, either a mode in which either of the elastic film 51 and the insulator film 52 is omitted to function as a vibrating plate or a mode in which the elastic film 51 and the insulator film 52 are omitted and only the first electrode 60 functions as a vibrating plate can be adopted.

[0045] On the substrate 10 (vibration plate 50) on which the piezoelectric element 300 is formed, a protection substrate 30 is joined by an adhesive 35. The protection substrate 30 has a manifold portion 32. At least a portion of the manifold 100 is constituted by the manifold portion 32. The manifold portion 32 of the present embodiment penetrates the protection substrate 30 in the thickness direction (Z direction), and is further formed across the width direction (+X direction) of the pressure generating chamber 12. Also, the manifold portion 32 communicates with the communication portion 15 of the substrate 10. By these structures, the manifold 100 which becomes a common ink chamber of each pressure generating chamber 12 is constituted.

[0046] On the protection substrate 30, a piezoelectric element holding portion 31 is formed in a region containing the piezoelectric element 300. The piezoelectric element holding portion 31 has a space to the extent that does not hinder the movement of the piezoelectric element 300. This space can be sealed or can not be sealed. On the protection substrate 30, a through-hole 33 is provided which penetrates the protection substrate 30 in the thickness direction (Z direction). The end portion of the lead electrode 90 is exposed inside the through-hole 33.

[0047] Although Si, SOI, glass, ceramic material, metal, resin, and the like can be cited as the material of the protection substrate 30, it is more preferable to be formed of a material having substantially the same thermal expansion rate as that of the substrate 10.

[0048] On the protection substrate 30, a drive circuit 120 which functions as a signal processing portion is fixed. The drive circuit 120 can use, for example, a circuit substrate or a semiconductor integrated circuit (IC: Integrated Circuit). The drive circuit 120 and the lead electrode 90 are electrically connected by a connection wiring 121 constituted by a conductive lead such as a joining lead which is inserted through the through-hole 33. The drive circuit 120 can be electrically connected to a printer controller 200 (refer to Figure 1 ). Such a drive circuit 120 functions as a control unit of the piezoelectric actuator device (piezoelectric element 300).

[0049] Further, on the protection substrate 30, a plastic substrate 40 constituted by a sealing film 41 and a fixing plate 42 is joined. The sealing film 41 is constituted by a material having low rigidity, and the fixing plate 42 can be constituted by a hard material such as metal. The region of the fixing plate 42 which opposes the manifold 100 becomes an opening portion 43 which is completely removed in the thickness direction (Z direction). One face (+Z direction side face) of the manifold 100 is sealed only by the sealing film 41 having flexibility.

[0050] Such a recording head 1 ejects ink droplets with the following action.

[0051] First, ink is taken in from an ink inlet connected to an external ink supply unit not shown, and the interior is filled with ink from the manifold 100 to the nozzle 21. Thereafter, a voltage is applied between each first electrode 60 and second electrode 80 corresponding to the pressure generating chamber 12 in accordance with a recording signal from the drive circuit 120, to cause the piezoelectric element 300 to deform in flexure. By this, the pressure in each pressure generating chamber 12 rises, thereby causing ink droplets to be ejected from the nozzle 21.

[0052] piezoelectric element

[0053] Next, the structure of the piezoelectric element 300 will be described with reference to the drawings. Figure 5 For Figure 4 enlarged cross-sectional view taken along line B-B' thereof.

[0054] As shown in the drawings, the piezoelectric element 300 is provided with: a substrate 10; a first electrode 60 formed on the substrate 10; a piezoelectric layer 70 formed on the first electrode 60, and containing potassium, sodium, and niobium; and a second electrode 80 formed on the piezoelectric layer 70.

[0055] On the substrate 10, there are provided pressure generating chambers 12 divided by a plurality of partition walls 11. By this structure, a movable portion of the piezoelectric element 300 is formed. The thickness of each element listed here is one example, and can be changed within a range not changing the gist of the present application.

[0056] The material of the first electrode 60 and the second electrode 80 is preferably a noble metal such as platinum (Pt) or iridium (Ir), or an oxide thereof. The material of the first electrode 60 and the material of the second electrode 80 can be any material having electrical conductivity. The material of the first electrode 60 and the material of the second electrode 80 can be the same or different.

[0057] The substrate 10 is, for example, a flat plate formed of a semiconductor or an insulator. The substrate 10 can be a single layer, or a structure in which a plurality of layers are stacked. The substrate 10 can also include a vibration plate that has flexibility and can deform (bend) in accordance with the change in the piezoelectric layer 70. As the material of the vibration plate, for example, silicon oxide, zirconium oxide, or a laminate thereof can be listed.

[0058] On the other face of the substrate 10 (+Z direction side face), a vibration plate 50 composed of an elastic film 51 and an insulator film 52 is formed as described above. It is preferable that the elastic film 51 be composed of, for example, silicon dioxide (SiO2), and the insulator film 52 contain, for example, zirconium oxide (ZrO2). By applying zirconium oxide as the insulator film 52, it is possible to increase the Young's modulus of the vibration plate 50 itself. As a result, it is possible to suppress the case where the vibration plate 50 is deflected by stress from the piezoelectric layer 70 or the second electrode 80 in a state where no voltage is applied. From this viewpoint, it is preferable that the insulator film 52 be composed of zirconium oxide.

[0059] The first electrode 60 is formed on the substrate 10 (on the vibration plate 50 in the present embodiment). Figure 5 The shape of the first electrode 60 is, for example, layered or thin film-like. The thickness (length in the Z axis direction) of the first electrode 60 is, for example, 50 nm or more and 300 nm or less. The planar shape (shape viewed from the Z axis direction) of the first electrode 60 is not particularly limited as long as it is a shape in which the piezoelectric layer 70 can be disposed between the first electrode 60 and the second electrode 80 when they are disposed in opposition to each other.

[0060] As the material of the first electrode 60, various metals such as nickel, iridium, platinum, and the like, conductive oxides thereof (for example, iridium oxide and the like), a composite oxide of strontium and ruthenium (SrRuO X : SRO), and a composite oxide of lanthanum and nickel (LaNiO X : LNO) can be exemplified. The first electrode 60 can be either a single-layer structure of the materials exemplified above or a structure in which a plurality of materials are laminated.

[0061] The first electrode 60 and the second electrode 80 form a pair, and thus can become one electrode (for example, a lower electrode formed below the piezoelectric layer 70) for applying a voltage to the piezoelectric layer 70.

[0062] In addition, the vibration plate 50 can be omitted, and the first electrode 60 can function as a vibration plate. That is, the first electrode 60 can have a function as one electrode for applying a voltage to the piezoelectric layer 70 and a function as a vibration plate that can be deformed in accordance with a change in the piezoelectric layer 70.

[0063] Further, between the first electrode 60 and the substrate 10, a layer that imparts adhesiveness between the two (for example, an adhesion layer 56) and a layer that imparts strength or conductivity can be formed. As examples of such a layer, layers of various metals such as titanium, nickel, iridium, platinum, and the like, and oxides thereof can be exemplified.

[0064] Further, it is preferable that a seed layer (also referred to as an orientation control layer) be provided between the first electrode 60 and the piezoelectric layer 70. The seed layer has a function of controlling the orientation of the crystal of the piezoelectric body constituting the piezoelectric layer 70. That is, by providing the seed layer, the crystal of the piezoelectric body constituting the piezoelectric layer 70 can be oriented preferentially in a predetermined plane orientation, as a result of which the hardness of the piezoelectric layer 70 can be improved sufficiently.

[0065] The piezoelectric layer 70 is formed on the first electrode 60. The thickness of the piezoelectric layer 70 is, for example, 50 nm or more and 2000 nm or less.

[0066] The piezoelectric layer 70 is formed by a solution method (also referred to as a liquid phase method or a wet method) such as a MOD method, a sol-gel method, or a vapor phase method such as a sputtering method. In the present embodiment, it is a composite oxide of a perovskite type represented by the general formula ABO3, which is formed by a solution method and contains potassium (K), sodium (Na), and niobium (Nb). That is, the piezoelectric layer 70 contains a piezoelectric material composed of a KNN-based composite oxide represented by the following formula (1).

[0067] (K X , Na 1-X )NbO3···(1)

[0068] (0.1≤X≤0.9)

[0069] The piezoelectric material constituting the piezoelectric layer 70 is not limited to the composition represented by the above formula (1) as long as it is a KNN-based composite oxide. For example, other metal elements (additives) can be contained in the A site and the B site of potassium sodium niobate. As examples of such additives, 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) can be listed.

[0070] One or more of such additives can be contained. In general, the amount of the additive is 20% or less, preferably 15% or less, and more preferably 10% or less, with respect to the total amount of the elements that are main components. Although the use of the additive makes it easy to achieve diversification of the structure and the function by improving various characteristics, from the viewpoint of exerting the characteristics of KNN, it is preferable that KNN be present in more than 80%. In addition, even in the case of a composite oxide containing these other elements, it is preferable that it be composed in such a way as to have a perovskite structure of ABO3 type.

[0071] Further, in the present specification, the "perovskite-type composite oxide containing K, Na, and Nb" is a "composite oxide of ABO3-type perovskite structure containing K, Na, and Nb", and is not limited only to the composite oxide of ABO3-type perovskite structure containing K, Na, and Nb. That is, in the present specification, the "perovskite-type composite oxide containing K, Na, and Nb" includes a piezoelectric material represented as a mixed crystal including the composite oxide of ABO3-type perovskite structure containing K, Na, and Nb (for example, the KNN-based composite oxide exemplified above), and other composite oxides having ABO3-type perovskite structure.

[0072] Although the other composite oxides are not limited in the scope of the present embodiment, it is preferable that a non-lead-based piezoelectric material not containing lead (Pb) be used. By doing so, a piezoelectric element 300 having excellent biocompatibility and less environmental load is obtained.

[0073] The piezoelectric layer 70 according to the present embodiment is a KNN-based piezoelectric thin film having a Young's modulus of 130 GPa or more. By setting the Young's modulus of the piezoelectric layer 70 to 130 GPa or more, it is possible to suppress a decrease in very excellent piezoelectric characteristics compared to conventional KNN thin films. Specifically, it is possible to suppress a decrease in efficiency (linearity) of the displacement amount of the vibrating plate even when high voltage (for example, 20 to 50 V) is applied. It is preferable that the Young's modulus of the piezoelectric layer 70 be 150 GPa or more. On the other hand, although the upper limit of the Young's modulus of the piezoelectric layer 70 is not particularly limited, it is possible to set it to 200 GPa or less because if the Young's modulus of the piezoelectric layer 70 is too large, it will interfere with the displacement itself.

[0074] If the Young's modulus of the piezoelectric layer 70 according to the present embodiment is 130 GPa or more, it is a high level. By increasing the Young's modulus in this way, it is possible to sufficiently harden the piezoelectric layer 70, and as a result, it is possible to suppress a decrease in efficiency of the displacement amount of the vibrating plate even when high voltage is applied, and to avoid deformation of the piezoelectric layer 70 itself. Further, by sufficiently hardening the piezoelectric layer 70, it is possible to suppress deformation caused by stress of the second electrode 80, and to reduce the initial deflection of the vibrating plate 50.

[0075] From such a viewpoint, it is preferable that the ratio of the Young's modulus of the piezoelectric layer 70 to the Young's modulus of the second electrode 80 be 0.8 or more and 1.0 or less. By providing the second electrode 80 and the piezoelectric layer 70 with a ratio within this range, it is possible to further suppress deformation of the piezoelectric layer 70 caused by stress of the second electrode 80.

[0076] Here, the Young's modulus of the piezoelectric layer 70 is measured by the following method.

[0077] The Young's modulus is measured based on nanoindentation measurement. In the present embodiment, the nanoindentation measurement is performed using UMIS-2000 manufactured by CSIRO. That is, the Young's modulus is calculated based on the load applied to the indenter and the projected area under the indenter when the indenter having a spherical tip is pressed into the surface of the piezoelectric layer 70.

[0078] Further, as described above, in order to suppress the decrease in the efficiency (linearity) of the displacement amount of the vibrating plate, it is more effective to sufficiently harden the piezoelectric layer 70. In order to increase the hardness of the piezoelectric layer 70, it is more effective to increase the density. Specifically, it is preferable to set the density of the piezoelectric layer 70 to 4.41 g / cm 3 or more, and 4.50 g / cm 3 or more. On the other hand, although the upper limit of the density of the piezoelectric layer 70 is not particularly limited, it can be set to 4.77 g / cm 3 or less from the viewpoint of not including foreign matters that do not have piezoelectricity.

[0079] The preferable control method of the Young's modulus and the density of the piezoelectric layer 70 will be described later.

[0080] The second electrode 80 is formed on the piezoelectric layer 70. The second electrode 80 is disposed in opposition to the first electrode 60 with the piezoelectric layer 70 interposed therebetween. The shape of the second electrode 80 is, for example, a layered or thin film shape. The thickness of the second electrode 80 is, for example, 10 nm or more and 500 nm or less. The planar shape of the second electrode 80 is not particularly limited as long as it is a shape in which the piezoelectric layer 70 can be disposed between the first electrode 60 and the second electrode 80 when they are disposed in opposition to each other.

[0081] As the material of the second electrode 80, for example, the materials listed above as the material of the first electrode 60 can be applied. However, in order to make the ratio of the Young's modulus of the piezoelectric layer 70 to the Young's modulus of the second electrode 80 satisfy the above range, it is preferable to use platinum (Pt) as the material of the second electrode 80.

[0082] As one of the functions of the second electrode 80, the following function can be listed, that is, it becomes a pair with the first electrode 60, and becomes the other electrode for applying a voltage to the piezoelectric layer 70 (for example, an upper electrode formed on the upper side of the piezoelectric layer 20).

[0083] According to the piezoelectric element 300 according to Embodiment 1 described above, by sufficiently increasing the Young's modulus of the piezoelectric layer 70, it is possible to improve the efficiency of the displacement amount at the time of high voltage (for example, 20 to 50 V) driving.

[0084] Further, although the inkjet recording head is described as an example of the liquid ejecting head in the above-described embodiments, the present application can be applied to the entire liquid ejecting head, and can be applied to a liquid ejecting head that ejects a liquid other than ink. As other liquid ejecting heads, for example, various recording heads used in image recording apparatuses such as printers, color material ejecting heads used in the manufacture of color filters of liquid crystal displays, electrode material ejecting heads used in the formation of electrodes of organic EL displays, FEDs (field emission displays), and the like, biological organic matter ejecting heads used in the manufacture of biochips, and the like can be listed.

[0085] Further, the present application is not limited to the piezoelectric element mounted in the liquid ejecting head, and can be applied to a piezoelectric element mounted in other piezoelectric element application devices. As an example of the piezoelectric element application device, an ultrasonic device, a motor, a pressure sensor, a pyroelectric element, a ferromagnetic element, and the like can be listed. Further, a completed body using such a piezoelectric element application device, for example, a liquid ejecting apparatus using the above-described liquid ejecting head, an ultrasonic sensor using the above-described ultrasonic device, an automatic device using the above-described motor as a driving source, an IR sensor using the above-described pyroelectric element, a ferromagnetic memory using the ferromagnetic element, and the like are also included in the piezoelectric element application device.

[0086] In particular, the piezoelectric element of the present application is more preferable as a piezoelectric element mounted in a sensor. As the sensor, for example, a gyro sensor, an ultrasonic sensor, a pressure sensor, a speed / acceleration sensor, and the like can be listed. In the case where the piezoelectric element of the present application is applied to a sensor, for example, by providing a voltage detection portion that detects a voltage output from the piezoelectric element 300 between the first electrode 60 and the second electrode 80, a sensor can be formed. In such a sensor, when the piezoelectric element 300 is deformed due to some external change (change in physical quantity), a voltage is generated along with the deformation. By detecting the voltage using the voltage detection portion, various physical quantities can be detected.

[0087] Next, an example of a manufacturing method of the piezoelectric element 300 will be described.

[0088] First, a substrate (silicon substrate) 10 is prepared, and an elastic film 51 composed of silicon dioxide (SiO2) is formed on the surface of the substrate 10 by heat oxidation of the substrate 10.

[0089] Next, a zirconium film is formed on the elastic film 51 by a sputtering method, an evaporation method, or the like, and an insulator film 52 composed of zirconia (Zr02) is obtained by heat-oxidizing the zirconium film. In this way, the vibrating plate 50 composed of the elastic film 51 and the insulator film 52 is formed on the substrate 10.

[0090] Next, a TiO X The adhesion layer 56 can be formed by a sputtering method and heat-oxidation of a Ti film, or the like. Next, a first electrode 60 composed of Pt is formed on the adhesion layer 56. The first electrode 60 can be appropriately selected depending on the electrode material, and can be formed by, for example, vapor deposition such as a sputtering method, a vacuum evaporation method (PVD method), a laser ablation method, or liquid deposition such as a spin coating method, or the like.

[0091] Next, a resist of a predetermined shape is formed on the first electrode 60 as a mask, and the adhesion layer 56 and the first electrode 60 are subjected to patterning. The patterning of the adhesion layer 56 and the first electrode 60 can be performed by, for example, dry etching such as reactive ion etching (RIE), ion milling, or wet etching using an etching solution. In addition, the shape in the patterning of the adhesion layer 56 and the first electrode 60 is not particularly limited.

[0092] Next, a multilayer piezoelectric film is formed on the first electrode 60.

[0093] The piezoelectric layer 70 is composed of the multilayer piezoelectric film. The piezoelectric layer 70 can be formed by, for example, a chemical solution method (wet method) in which a solution (precursor solution) containing a metal complex is applied and dried, and then heat-treated at a high temperature to obtain a metal oxide. In addition to this, the piezoelectric layer 70 can be formed by a laser ablation method, a sputtering method, a pulsed laser deposition method (PLD method), a CVD (Chemical Vapor Deposition) method, an aerosol deposition method, or the like. In the present embodiment, from the viewpoint of orienting the face direction of the piezoelectric layer 70 in the (100) direction and increasing the Young's modulus of the piezoelectric layer 70, it is preferable to use the wet method (liquid phase method).

[0094] Here, the wet method (liquid phase method) refers to a method of forming a film by a chemical solution method such as a MOD method, a sol-gel method, or the like, and is a concept that is distinguished from a vapor phase method such as a sputtering method. In the present embodiment, as long as it is a method that can form a piezoelectric layer 70 having a face direction oriented in the (100) direction, a vapor phase method can also be used.

[0095] For example, the piezoelectric layer 70 formed by the wet method (liquid phase method) has a plurality of piezoelectric films 74 formed by a series of processes of a process of applying a precursor solution to form a precursor film (application process), a process of drying the precursor film (drying process), a process of heating the dried precursor film to remove a solvent (solvent removal process), and a process of firing the solvent-removed precursor film (firing process). That is, the piezoelectric layer 70 is formed by repeating the series of processes from the application process to the firing process a plurality of times. In addition, in the series of processes, the firing process can be performed after repeating the processes from the application process to the solvent removal process a plurality of times.

[0096] A layer or film formed by the wet method has an interface. A trace of application or firing remains on a layer or film formed by the wet method, and such a trace becomes an interface that can be confirmed by observing a cross section thereof or analyzing a concentration distribution of elements in the layer (or film). Although the interface strictly refers to a boundary between layers or films, it refers to a vicinity of a boundary of a layer or film here. In a case where a cross section of a layer or film formed by the wet method is observed with an electron microscope or the like, such an interface is confirmed as a portion that is darker in color than other layers or films or a portion that is lighter in color than other layers or films in the vicinity of a boundary with an adjacent layer or film. Further, in a case where a concentration distribution of elements is analyzed, such an interface can be confirmed as a portion that is higher in concentration of elements than other layers or films or a portion that is lower in concentration of elements than other layers or films in the vicinity of a boundary with an adjacent layer or film. Since the piezoelectric layer 70 is formed by repeating the series of processes from the application process to the firing process a plurality of times or performing the firing process after repeating the processes from the application process to the solvent removal process a plurality of times (comprises a plurality of piezoelectric films 74), a plurality of interfaces corresponding to the respective piezoelectric films 74 are present.

[0097] Specific steps in a case where the piezoelectric layer 70 is formed by the wet method (liquid phase method) are, for example, as follows.

[0098] First, a precursor solution containing a predetermined metal complex is adjusted. The precursor solution is a liquid formed by dissolving or dispersing a metal complex that can form a complex oxide containing K, Na, and Nb by firing in an organic solvent. At this time, a metal complex containing an additive such as Mn can be further mixed. By mixing the precursor solution with a metal complex containing Mn, the Young's modulus of the obtained piezoelectric layer 70 can be further increased.

[0099] As the metal complex containing potassium (K), there can be mentioned potassium 2-ethylhexanoate, potassium acetate, and the like. As the metal complex containing sodium (Na), there can be mentioned sodium 2-ethylhexanoate, sodium acetate, and the like. As the metal complex containing niobium (Nb), there can be mentioned niobium 2-ethylhexanoate, niobium pentaethoxide, and the like. In the case where Mn is added as an additive, as the metal complex containing Mn, there can be mentioned manganese 2-ethylhexanoate, and the like. At this time, two or more kinds of metal complexes can be used together. For example, as the metal complex containing potassium (K), potassium 2-ethylhexanoate and potassium acetate can be used together. As the solvent, there can be mentioned 2-n-butoxyethanol or n-octane or a mixed solvent thereof, and the like. The precursor solution can also contain an additive for stabilizing dispersion of the metal complex containing K, Na, and Nb. As such an additive, there can be mentioned 2-ethylhexanoic acid, and the like.

[0100] Then, the precursor solution described above is applied to the substrate 10 on which the elastic film 51, the insulator film 52, and the first electrode 60 are formed, thereby forming a precursor film (application step).

[0101] Next, the precursor film is heated to a predetermined temperature, for example, about 130°C to 250°C, and is dried for a fixed time (drying step).

[0102] The temperature increase rate in the drying step is preferably 30°C to 350°C / sec. By using the solution method and performing the firing of the piezoelectric film at such a temperature increase rate, it is possible to realize the piezoelectric layer 70 which is not a pseudo-cubic crystal. Further, the "temperature increase rate" described here is defined as the rate of change of temperature from 350°C to the target firing temperature.

[0103] Next, the precursor film after drying is heated to a predetermined temperature, for example, 350°C to 500°C, and is held at this temperature for a fixed time, thereby performing the debinding (debinding step).

[0104] From the viewpoint of increasing the Young's modulus of the piezoelectric layer 70, the heating temperature in the debinding step is preferably set to 350°C or higher. More preferably, it is set to 370°C or higher. On the other hand, if the heating temperature in the debinding step is too high, there is a possibility that foreign matter will be formed due to an undesirable reaction. Therefore, the heating temperature is preferably set to 420°C or lower.

[0105] From the viewpoint of increasing the Young's modulus of the piezoelectric layer 70, the heating time in the debinding step is preferably set to 2 minutes or longer. More preferably, it is set to 3 minutes or longer. On the other hand, if the heating time in the debinding step is too long, there is a possibility that the carbon component which has been removed by debinding will be attached again. Therefore, the heating time is preferably set to 7 minutes or shorter.

[0106] Finally, the defatted precursor film is crystallized by heating it to a high temperature, for example, about 650°C to 800°C, and holding it at that temperature for a fixed time. In this way, the piezoelectric film is completed (firing step).

[0107] In the firing step, it is preferable to crystallize the precursor film while applying pressure. By performing the firing step while applying pressure, it is possible to increase the hardness of the piezoelectric layer 70, and further increase the Young's modulus. As the pressure application conditions, it is preferable to set the pressure to be 0.005 MPa or more with respect to atmospheric pressure. On the other hand, if the pressure during firing is too high, it is possible that the process exhaust gas will be excessively incorporated into the film, causing an unexpected reaction. Therefore, the pressure during pressure application is preferably set to be 0.9 MPa or less with respect to atmospheric pressure.

[0108] From the viewpoint of increasing the Young's modulus of the piezoelectric layer 70, the heating temperature in the firing step is preferably set to be 650°C or more. More preferably, it is 700°C or more. On the other hand, if the heating temperature in the firing step is too high, it is possible that diffusion of alkali metal components to the lower electrode, dissolution of the metal material constituting the lower electrode, and the like will occur. Therefore, the heating temperature is preferably set to be 760°C or less.

[0109] From the viewpoint of increasing the Young's modulus of the piezoelectric layer 70, the heating time in the firing step is preferably set to be 1 minute or more. More preferably, it is 2 minutes or more. On the other hand, if the heating time in the firing step is too long, it is possible that the alkali metal components will diffuse to the lower electrode. Therefore, the heating time is preferably set to be 8 minutes or less.

[0110] As the heating device used in the drying step, the defatting step, and the firing step, for example, an RTA (Rapid Thermal Annealing) device or a hot plate, which heats by irradiation of infrared lamps, or the like can be cited. The above-described steps are repeatedly performed a plurality of times, thereby forming the piezoelectric layer 70 composed of a plurality of piezoelectric films. In addition, in the series of steps from the coating step to the firing step, the firing step can be performed after the steps from the coating step to the defatting step have been repeatedly performed a plurality of times.

[0111] Further, before and after forming the second electrode 80 on the piezoelectric layer 70, a re-heating treatment (post-annealing) can be performed as needed in the temperature range of 600°C to 800°C. By performing the post-annealing in this way, it is possible to form a good interface between the piezoelectric layer 70 and the first electrode, and a good interface between the piezoelectric layer 70 and the second electrode 80. In addition, it is possible to improve the crystallinity of the piezoelectric layer 70, and further increase the Young's modulus.

[0112] After the firing process, the piezoelectric layer 70 composed of a plurality of piezoelectric films is image-formed in the shape shown in FIG. 1. The image formation can be performed by dry etching such as reactive ion etching, ion milling, or wet etching using an etching solution. Figure 5 The second electrode 80 can be formed by the same method as the first electrode 60.

[0113] After that, the second electrode 80 is formed on the piezoelectric layer 70. The second electrode 80 can be formed by the same method as the first electrode 60.

[0114] By the above process, the piezoelectric element 300 provided with the first electrode 60, the piezoelectric layer 70, and the second electrode 80 is manufactured.

[0115] Example

[0116] Hereinafter, the present application will be described in more detail by examples, but the present application is not limited to these examples at all.

[0117] Example 1

[0118] First, the surface of a silicon substrate (6 inches) as a substrate was heat-oxidized to form a spring film (1370 nm) composed of silicon dioxide on the substrate. In addition, a zirconium film was formed on the spring film by a sputtering method and heat-oxidized to form an insulator film (400 nm) composed of zirconia (Zr02). Thus, a vibrating plate composed of the spring film and the insulator film was formed on the substrate.

[0119] Next, a first electrode (135 nm) composed of platinum (Pt) was formed on the vibrating plate by a sputtering method, and a resist of a predetermined shape was formed as a mask, and the first electrode 60 was pattern-formed by RIE.

[0120] Next, the piezoelectric layer was formed on the first electrode by the following steps.

[0121] First, a precursor solution composed of potassium 2-ethylhexanoate, sodium 2-ethylhexanoate, lithium 2-ethylhexanoate, niobium 2-ethylhexanoate, and manganese 2-ethylhexanoate was used, and coated on the substrate by a spin coating method to form a precursor film (coating process).

[0122] After that, the precursor film was dried at 180°C (drying process), and then, debinding was performed at 380°C for 3 minutes (debinding process).

[0123] Next, the degreased precursor film was subjected to RTA (Rapid Themal Annealing) at 750°C for 3 minutes under a pressurized atmosphere of 0.01 MPa relative to atmospheric pressure, thereby forming a piezoelectric film (firing process). This process from coating to firing was repeated multiple times to produce a piezoelectric layer with a total thickness of 1060 nm and a Young's modulus of 155 GPa, consisting of multiple piezoelectric films. The Young's modulus was measured using nanoindentation, as described above.

[0124] Finally, a second electrode made of platinum (Pt) is formed on the piezoelectric layer in the same manner as the first electrode, thereby obtaining a piezoelectric element.

[0125] Comparative Example 1

[0126] Except for setting the Young's modulus of the piezoelectric layer to 125 GPa and the total film thickness to 1200 nm, everything else is the same as in Example 1.

[0127] For each of the above embodiments and comparative examples, the initial deflection of the vibrating plate and the displacement of the vibrating plate when voltage is applied were investigated. (See Table 1.) Figure 6A , Figure 6B The results are shown in the figure.

[0128] In addition, the initial deflection is determined in the following manner.

[0129] Initial deflection

[0130] The displacement (initial deflection) when voltage was applied was determined for the piezoelectric element of Example 1 and Comparative Example 1. Here, the displacement at room temperature (25°C) was determined using a displacement measuring device (laser Doppler displacement meter).

[0131] Table 1

[0132] Initial deflection (nm) Example 1 526 Comparative Example 1 607

[0133] (Experimental Results)

[0134] As shown in Table 1, Example 1 was able to reduce the initial deflection by about 13% compared to Comparative Example 1.

[0135] Figure 6A The displacement of the vibrating plate when voltage is applied in Example 1 and Comparative Example 1 is indicated. Figure 6B The efficiency (linearity) of the displacement of the vibrating plate when the voltage is applied in Example 1 and Comparative Example 1 is shown. Additionally, although... Figure 6B The vertical axis represents "displacement / voltage", but the displacement is normalized to 1 when the driving voltage is 10V.

[0136] Although the one of Example 1 obtained a larger displacement amount compared with Comparative Example 1 in the region of 20 V or more as shown in FIG. 6, a larger difference was not found between Example 1 and Comparative Example 1. On the other hand, as shown in FIG. 7, it was known that the one of Example 1 more successfully suppressed the efficiency (linearity) of the displacement amount at a high voltage compared with Comparative Example 1, and the one of Example 1 was a piezoelectric element that was excellent in efficiency even at a high voltage. Figure 6A Figure 6B Figure 6B

[0137] Explanation of symbols

[0138] I... inkjet recording device (liquid ejection device); II... inkjet recording head unit (head unit); 1... inkjet recording head (liquid ejection head); 10... substrate; 12... pressure generating chamber; 13... ink supply channel; 14... communication channel; 15... communication portion; 20... nozzle plate; 21... nozzle; 30... protective substrate; 31... piezoelectric element holding portion; 32... manifold portion; 40... plastic substrate; 50... vibration plate; 51... elastic film; 52... insulator film; 60... first electrode; 70... piezoelectric layer; 80... second electrode; 90... lead electrode; 100... manifold; 300... piezoelectric element.​​

Claims

1. A piezoelectric element, characterized in that, have: First electrode; A piezoelectric layer is formed above the first electrode; A second electrode is formed above the piezoelectric layer. The piezoelectric layer comprises potassium, sodium, and niobium, and The Young's modulus of the piezoelectric layer, measured by nanoindentation, exceeds 130 GPa.

2. The piezoelectric element as described in claim 1, characterized in that, The ratio of the Young's modulus of the piezoelectric layer to the Young's modulus of the second electrode is greater than 0.8 and less than 1.

3. The piezoelectric element as described in claim 1 or 2, characterized in that, It also includes a substrate, which is disposed on the opposite side of the piezoelectric layer, separated from the first electrode. The substrate contains zirconium oxide.

4. A head chip, characterized in that, have: A nozzle plate, which has nozzles that eject liquid droplets; A pressure generating chamber, which is connected to the nozzle; A flow channel forming substrate is disposed on the nozzle plate and forms the pressure generating chamber; A vibrating plate that forms part of the wall of the pressure generating chamber; The piezoelectric element according to claim 1 or 2 is disposed on the vibrating plate; The voltage application section applies a voltage to the piezoelectric element.

5. A liquid injection device, characterized in that, have: A conveying unit that transports the medium; A droplet ejector head that applies droplets onto the medium. The droplet ejector head has the head chip as described in claim 4.

6. A sensor, characterized in that, have: The piezoelectric element according to any one of claims 1 to 3; The voltage detection unit detects the voltage output from the piezoelectric element.

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