Actuator, liquid ejection head, and printer

Abstract

To provide an actuator that can suppress a decrease in the increment of the displacement of a diaphragm even when an increased voltage is applied between a first electrode and a second electrode.SOLUTION: An actuator includes a vibration plate, a first electrode provided above the vibration plate, a piezoelectric layer provided above the first electrode and including a complex oxide having a perovskite structure, and a second electrode provided above the piezoelectric layer, and the remanent polarization of the piezoelectric layer is 0.535 times or less of a spontaneous polarization of the piezoelectric layer.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an actuator, a liquid ejection head, and a printer.

Background Art

[0002] An actuator including a diaphragm and a piezoelectric element is applied to, for example, a liquid ejection head of an inkjet printer.

[0003] For example, Patent Document 1 describes a piezoelectric actuator including a diaphragm and a piezoelectric element including a piezoelectric thin film having a crystal structure in which the directions of spontaneous polarization are aligned in a certain direction.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the piezoelectric actuator as described above, as the displacement amount of the diaphragm increases, the increase in the displacement amount of the diaphragm with respect to the increase in the displacement amount of the piezoelectric thin film decreases. Therefore, there is a problem that as the voltage applied to the piezoelectric element increases, the increase in the displacement amount of the diaphragm decreases.

Means for Solving the Problems

[0006] One aspect of the actuator according to the present invention is a diaphragm, a first electrode provided above the diaphragm, a piezoelectric layer provided above the first electrode and including a complex oxide having a perovskite structure, a second electrode provided above the piezoelectric layer, and includes The remanent polarization of the piezoelectric layer is 0.535 times or less of the spontaneous polarization of the piezoelectric layer.

[0007] One aspect of the liquid ejection device according to the present invention is One aspect of the actuator, and A nozzle plate in which nozzle holes are formed, and including The substrate is provided between the nozzle plate and the diaphragm, and a pressure generation chamber communicating with the nozzle holes is formed.

[0008] One aspect of the printer according to the present invention is The liquid ejection head, and A transport mechanism that relatively moves a recording medium with respect to the liquid ejection head, and A control unit that controls the liquid ejection head and the transport mechanism, and including.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

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Figure 8

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Figure 10

Figure 11

Figure 12

Figure 13

[0010] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the embodiments described below do not unduly limit the content of the present invention described in the claims. Also, not all of the configurations described below are essential components of the present invention.

[0011] 1. Actuator 1.1. Configuration First, the actuator according to the present embodiment will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing the actuator 100 according to the present embodiment.

[0012] As shown in FIG. 1, the actuator 100 includes a diaphragm 20 and a piezoelectric element 30. The actuator 100 is provided on a substrate 10.

[0013] The substrate 10 is, for example, a silicon substrate. In the illustrated example, an opening 12 is formed in the substrate 10. When the actuator 100 is applied to a liquid ejection head, the opening 12 serves as a pressure generation chamber that stores the liquid ejected from the liquid ejection head and applies pressure to the supplied liquid.

[0014] The diaphragm 20 is provided on the substrate 10. The diaphragm 20 is provided between the substrate 10 and the piezoelectric element 30. In the illustrated example, the diaphragm 20 closes the opening 12. The diaphragm 20 has, for example, a first layer 22 provided on the substrate 10 and a second layer 24 provided on the first layer 22. The first layer 22 is, for example, a silicon oxide layer. The second layer 24 is, for example, a zirconium oxide layer. The diaphragm 20 has flexibility. The diaphragm 20 deforms in response to the deformation of the piezoelectric element 30.

[0015] The piezoelectric element 30 is provided above the diaphragm 20. In the illustrated example, the piezoelectric element 30 is directly provided on the diaphragm 20. The piezoelectric element 30 includes, for example, a first electrode 32, a seed layer 34, a piezoelectric layer 36, and a second electrode 38.

[0016] In the description according to the present invention, when the term "above" is used, for example, in the case of "forming another specific thing (hereinafter referred to as "B") "above" a specific thing (hereinafter referred to as "A"), it includes both the case of directly forming B on A and the case of forming B on A via another thing. Therefore, the term "above" is used.

[0017] The first electrode 32 is provided above the diaphragm 20. In the illustrated example, the first electrode 32 , is directly provided on the diaphragm 20. The first electrode 32 is provided between the diaphragm 20 and the seed layer 34. The shape of the first electrode 32 is, for example, layer-like. The thickness of the first electrode 32 is, for example, 3 nm or more and 300 nm or less. The first electrode 32 is, for example, a metal layer such as a platinum layer, an iridium layer, a titanium layer, a ruthenium layer, or a conductive oxide layer thereof. The first electrode 32 may have a structure in which a plurality of the layers exemplified above are laminated. The first electrode 32 may be a laminated structure of a platinum layer and an iridium layer from the diaphragm 20 side. The first electrode 32 is one of the electrodes for applying a voltage to the piezoelectric layer 36.

[0018] Although not shown in the drawings, an adhesion layer may be provided between the diaphragm 20 and the first electrode 32 in order to improve the adhesion between the diaphragm 20 and the first electrode 32. The adhesion layer is, for example, a titanium layer, a titanium oxide layer, or the like.

[0019] The seed layer 34 is provided on the first electrode 32. The seed layer 34 is provided between the first electrode 32 and the piezoelectric layer 36. In the illustrated example, the seed layer 34 is further provided on the diaphragm 20. The thickness of the seed layer 34 is, for example, 5 nm or more and 100 nm or less, preferably 10 nm or more and 50 nm or less.

[0020] The seed layer 34 is, for example, a perovskite-type composite oxide containing bismuth (Bi), iron (Fe), and titanium (Ti). The seed layer 34 may be a bismuth iron titanate (Bi(Fe,Ti)O3:BFT) layer. The seed layer 34 may be a BFT layer to which lead (Pb) or the like is added. When lead is added, the lead content in the seed layer 34 is 0.1 mass% or less. Since the seed layer 34 has the same perovskite-type structure as the piezoelectric layer 36, the orientation, lattice constant, and crystal structure of the piezoelectric layer 36 can be easily controlled.

[0021] The piezoelectric layer 36 is provided above the first electrode 32. In the illustrated example, the piezoelectric layer 36 is provided on the first electrode 32 via the seed layer 34. The piezoelectric layer 36 is directly provided on the seed layer 34. The piezoelectric layer 36 is provided between the seed layer 34 and the second electrode 38. The piezoelectric layer 36 is, for example, composed of a plurality of crystal layers laminated. The thickness of the piezoelectric layer 36 is, for example, 100 nm or more and 3 μm or less, preferably 200 nm or more and 2 μm or less.

[0022] The piezoelectric layer 36 contains a perovskite-type composite oxide. The piezoelectric layer 36 may be composed of a perovskite-type composite oxide. The composite oxide may be composed of a ferroelectric. A "ferroelectric" is a substance in which electric dipoles are aligned even without an external electric field, and the direction of the dipoles can be changed by an electric field.

[0023] The piezoelectric layer 36 contains, for example, potassium (K), sodium (Na), and niobium (Nb). The piezoelectric layer 36 is, for example, a potassium sodium niobate ((K,Na)NbO3:KNN) layer. The piezoelectric layer 36 may be a KNN layer to which additives such as manganese (Mn) are added. If the piezoelectric layer 36 is a KNN layer, an environmentally friendly lead-free piezoelectric layer 36 can be formed.

[0024] Note that the piezoelectric layer 36 is not limited to the KNN layer. The piezoelectric layer 36 may be, for example, a lead-based piezoelectric layer such as a lead zirconate titanate (Pb(Zr,Ti)O3:PZT) layer or a lead zirconate titanate niobate (Pb(Zr,Ti,Nb)O3:PZTN) layer. Or, the piezoelectric layer 36 may be a non-lead-based piezoelectric layer other than the KNN layer.

[0025] The lattice constant in the in-plane direction of the piezoelectric layer 36 is, for example, smaller than the lattice constant in the in-plane direction of the seed layer 34. The "in-plane direction" is a direction orthogonal to the thickness direction of the substrate 10. When the material constituting the piezoelectric layer 36 is KNN, the lattice constant in the in-plane direction is the length in the a-axis direction.

[0026] A tensile stress is generated in the piezoelectric layer 36. The tensile stress of the piezoelectric layer 36 is, for example, 261 MPa or more and 1000 MPa or less. The tensile stress of the piezoelectric layer 36 is generated, for example, due to the difference between the lattice constant in the in-plane direction of the piezoelectric layer 36 and the lattice constant in the in-plane direction of the seed layer 34.

[0027] The second electrode 38 is provided above the piezoelectric layer 36. In the illustrated example, the second electrode 38 is provided directly on the piezoelectric layer 36. The shape of the second electrode 38 is, for example, layered. The thickness of the second electrode 38 is, for example, 3 nm or more and 300 nm or less. The second electrode 38 is, for example, a metal layer such as a platinum layer, an iridium layer, a titanium layer, a ruthenium layer, or a conductive oxide layer thereof. The second electrode 38 may have a structure in which a plurality of the layers exemplified above are laminated. The second electrode 38 is one of the electrodes for applying a voltage to the piezoelectric layer 36.

[0028] 1.2. Hysteresis Curve FIG. 2 is a diagram for explaining the hysteresis curve in the piezoelectric layer 36. The electric field E on the horizontal axis of FIG. 2 is the electric field generated in the piezoelectric layer 36 by applying a voltage between the first electrode 32 and the second electrode 38. The polarization amount P on the vertical axis of FIG. 2 is the amount of poles generated in the piezoelectric layer 36 by the electric field E.

[0029] The remanent polarization Pr is the polarization amount P when the electric field E is 0 kV / cm. The spontaneous polarization Ps is the polarization amount excluding the component due to the dielectric constant contribution when the ferroelectric constituting the piezoelectric layer 36 is completely polarized. Hereinafter, the intercept of the tangent line T of the hysteresis curve at the maximum electric field Emax, that is, E = 0, is defined as the spontaneous polarization Ps. Note that the maximum electric field Emax is the electric field generated in the piezoelectric layer 36 when the applied voltage between the first electrode 32 and the second electrode 38 is maximized.

[0030] The remanent polarization Pr is, for example, 12.2 μC / cm 2 or less, preferably 12.0 μC / cm 2 or less. The remanent polarization Pr is, for example, 0.8 μC / cm 2 or more, preferably 1.0 μC / cm 2 or more, more preferably 1.2 μC / cm 2 or more.

[0031] The spontaneous polarization Ps is larger than the remanent polarization Pr. The spontaneous polarization Ps is, for example, 23.2 μC / cm 2 or less, preferably 23.0 μC / cm2 The following is the case. The spontaneous polarization Ps is, for example, 5.0 μC / cm 2 or more, preferably 7.0 μC / cm 2 or more, and more preferably 8.0 μC / cm 2 or more.

[0032] The remanent polarization Pr is 0.535 times or less of the spontaneous polarization Ps, preferably 0.521 times or less. The remanent polarization Pr is, for example, 0.10 times or more of the spontaneous polarization Ps, preferably 0.122 times or more, and more preferably 0.15 times or more.

[0033] When the electric field E generated in the piezoelectric layer 36 is increased by 10% from 210 kV / cm, the increase rate of the displacement amount of the diaphragm 20 is, for example, 0.94 or more with respect to the decrease rate of the displacement amount of the diaphragm 20 when the electric field E is decreased by 10% from 210 kV / cm. In other words, the increase rate of the displacement amount of the diaphragm 20 when the electric field E is increased from 210 kV / cm to 231 kV / cm is 0.94 or more with respect to the decrease rate of the displacement amount of the diaphragm 20 when the electric field E is decreased from 210 kV / cm to 189 kV / cm.

[0034] 1.3. Effects In the actuator 100, a diaphragm 20, a first electrode 32 provided above the diaphragm 20, and a piezoelectric body layer 36 provided above the first electrode 32 and containing a complex oxide having a perovskite structure, and a second electrode 38 provided above the piezoelectric body layer 36 are included. The remanent polarization Pr of the piezoelectric body layer 36 is 0.535 times or less of the spontaneous polarization Ps of the piezoelectric body layer 36. Therefore, in the actuator 100, as shown in the "Examples and Comparative Examples" described later, the linearity of the hysteresis curve can be enhanced. Therefore, even if the applied voltage between the first electrode 32 and the second electrode 38 is increased, an increase in the displacement amount of the diaphragm 20 can be suppressed from becoming small. Thus, the design of the operating voltage becomes easy.

[0035] In the actuator 100, the remanent polarization Pr is 12.2 μC / cm 2 or less, and the spontaneous polarization Ps is 23.2 μC / cm2 It is as follows. Therefore, in the actuator 100, the residual polarization Pr can be made 0.535 times or less of the spontaneous polarization Ps.

[0036] In the actuator 100, the increase rate of the displacement amount of the diaphragm 20 when the electric field E generated in the piezoelectric layer 36 is increased by 10% from 210 kV / cm is 0.94 or more with respect to the decrease rate of the displacement amount of the diaphragm 20 when the electric field E is decreased by 10% from 210 kV / cm. Therefore, in the actuator 100, the linearity of the hysteresis curve can be enhanced.

[0037] In the actuator 100, the tensile stress of the piezoelectric layer 36 is 261 MPa or more. Therefore, in the actuator 100, the component in the thickness direction of the polarization generated in the piezoelectric layer 36 can be reduced. Thereby, the residual polarization Pr can be reduced, and the linearity of the hysteresis curve can be enhanced.

[0038] The actuator 100 includes a seed layer 34 provided between the first electrode 32 and the piezoelectric layer 36, and the lattice constant of the piezoelectric layer 36 in the in-plane direction is smaller than the lattice constant of the seed layer 34 in the in-plane direction. Therefore, in the actuator 100, a tensile stress can be generated in the piezoelectric layer 36.

[0039] 2. Method for manufacturing an actuator Next, a method for manufacturing the actuator 100 according to the present embodiment will be described with reference to the drawings. FIG. 3 is a cross-sectional view schematically showing the manufacturing process of the actuator 100 according to the present embodiment.

[0040] As shown in FIG. 3, a first layer 22 is formed on a substrate 10. Next, a second layer 24 is formed on the first layer 22. The first layer 22 is formed, for example, by thermally oxidizing the substrate 10 which is a silicon substrate. The second layer 24 is formed by forming a zirconium layer on the first layer 22 by a sputtering method or the like and thermally oxidizing the zirconium layer. By this process, a diaphragm 20 having the first layer 22 and the second layer 24 can be formed.

[0041] Next, a first electrode 32 is formed on the diaphragm 20. The first electrode 32 is formed, for example, by a sputtering method or a vacuum evaporation method. Next, the first electrode 32 is patterned. The patterning is performed, for example, by photolithography and etching.

[0042] As shown in FIG. 1, a seed layer 34 is formed on the first electrode 32. The seed layer 34 is formed by a chemical solution deposition (CSD) method such as a sol-gel method or a MOD (Metal Organic Deposition) method. Hereinafter, a method for forming the seed layer 34 which is a BFT layer will be described.

[0043] For example, a metal complex containing bismuth, a metal complex containing iron, and a metal complex containing tantalum are dissolved or dispersed in an organic solvent to prepare a precursor solution. Examples of the metal complex containing bismuth include bismuth 2-ethylhexanoate, bismuth acetate, etc. Examples of the metal complex containing iron include iron 2-ethylhexanoate, iron acetate, tris(acetylacet tonato)iron, etc. Examples of the metal complex containing tantalum include pentaethoxytantalum, etc. Note that two or more types of metal complexes may be used in combination. For example, as the metal complex containing bismuth, bismuth 2-ethylhexanoate and bismuth acetate may be used in combination.

[0044] Examples of the organic solvent used for preparing the precursor solution include propanol, butanol, pentanol, hexanol, octanol, ethylene glycol, propylene glycol, octane, decane, cyclohexane, xylene, toluene, tetrahydrofuran, acetic acid, octylic acid, 2-n-butoxyethanol, n-octane, etc., or a mixed solvent thereof. The precursor solution may contain an additive for stabilizing the dispersion of each metal complex. Examples of such an additive include 2-ethylhexanoic acid and diethanolamine.

[0045] Next, the prepared precursor solution is applied onto the first electrode 32 and the diaphragm 20 using a spin coating method or the like to form a precursor layer. Next, the precursor layer is heated at, for example, 130°C or higher and 250°C or lower for a certain period of time to be dried, and further, the dried precursor layer is heated at, for example, 300°C or higher and 450°C or lower for a certain period of time to be degreased. Next, the degreased precursor layer is crystallized by firing at, for example, 550°C or higher and 800°C or lower.

[0046] The heating device used for drying and degreasing the precursor layer is, for example, a hot plate. The heating device used for firing the precursor layer is, for example, a lamp annealing device.

[0047] Through the above steps, the seed layer 34 can be formed.

[0048] Next, a piezoelectric layer 36 is formed on the seed layer 34. The piezoelectric layer 36 is formed, for example, by the same chemical solution deposition method as the seed layer 34. Hereinafter, a method for forming the piezoelectric layer 36 which is a KNN layer added with manganese will be described.

[0049] For example, a metal complex containing potassium, a metal complex containing sodium, a metal complex containing niobium, and a metal complex containing manganese are dissolved or dispersed in an organic solvent to prepare a precursor solution.

[0050] Examples of the metal complex containing potassium include potassium 2-ethylhexanoate, potassium acetate, etc. Examples of the metal complex containing sodium include sodium 2-ethylhexanoate, sodium acetate, etc. Examples of the metal complex containing niobium include niobium 2-ethylhexanoate, pentaethoxynbium, pentabutoxynbium, etc. Examples of the metal complex containing manganese include manganese 2-ethylhexanoate, etc. Note that two or more metal complexes may be used in combination. As the solvent, for example, the above materials mentioned for the formation of the seed layer 34 are used.

[0051] Next, the prepared precursor solution is applied onto the first electrode 32 using a spin coating method or the like to form a precursor layer. Next, the precursor layer is heated at, for example, 130°C or higher and 250°C or lower for a certain period of time to be dried, and further, the dried precursor layer is heated at, for example, 300°C or higher and 450°C or lower for a certain period of time to be held for degreasing. Next, the degreased precursor layer is fired at, for example, 550°C or higher and 800°C or lower to be crystallized to form a crystal layer. The heating device for the precursor layer uses, for example, the above-mentioned device mentioned for the formation of the seed layer 34.

[0052] Next, the crystal layer is cooled. Specifically, the crystal layer is cooled at a rate of 3.0°C / second or higher, preferably 5.0°C / second or higher. By cooling the crystal layer at such a rate, as shown in FIG. 4, tensile stress can be generated in the crystal structure 36a of the crystal layer.

[0053] For example, when the crystal layer is slowly cooled at 0.3°C / second, since the heat of the crystal layer is sufficiently transferred to the substrate before cooling, the substrate also shrinks together with the crystal layer. Therefore, it is difficult for tensile stress to occur in the crystal layer.

[0054] On the one hand, when the crystal layer is rapidly cooled, the crystal layer is selectively contracted because it is cooled before the heat of the crystal layer is sufficiently transferred to the substrate. Therefore, the crystal layer is pulled in the in-plane direction by the substrate, and a tensile stress F is generated. When the tensile stress F is large, the residual polarization Pr becomes small, and the linearity of the hysteresis curve becomes high. For the cooling of the crystal layer, for example, air cooling or water cooling using circulating cooling water is used. Note that FIG. 4 is a diagram for explaining the tensile stress F generated in the crystal structure 36a, and the crystal structure 36a is shown in a simplified manner.

[0055] The series of steps from the application of the above precursor solution to the firing of the precursor layer are repeated a plurality of times. Thereby, a piezoelectric layer 36 composed of a plurality of crystal layers can be formed. The number of crystal layers constituting the piezoelectric layer 36 is, for example, 5 or more and 20 or less, preferably 10 or more and 15 or less.

[0056] The piezoelectric layer 36 can be formed by the above steps.

[0057] Note that the method for forming the piezoelectric layer 36 and the seed layer 34 is not limited to the chemical solution deposition method, and a physical vapor deposition (PVD) method may be used. Examples of the physical vapor deposition method include a sputtering method and a laser ablation method.

[0058] Next, a second electrode 38 is formed on the piezoelectric layer 36. The second electrode 38 is formed, for example, by a sputtering method or a vacuum evaporation method. Next, the second electrode 38, the piezoelectric layer 36, and the seed layer 34 are patterned. The patterning is performed, for example, by photolithography and etching. By patterning the second electrode 38, the piezoelectric layer 36, and the seed layer 34 together, the manufacturing process can be shortened. Note that the second electrode 38, the piezoelectric layer 36, and the seed layer 34 may be patterned in separate steps.

[0059] Next, the lower surface of the substrate 10 is patterned to form the opening 12. The patterning is performed, for example, by photolithography and etching. Note that before performing the patterning, the lower surface of the substrate 10 may be ground and polished.

[0060] Through the above steps, the actuator 100 can be manufactured.

[0061] 3. Liquid ejection head Next, the liquid ejection head according to the present embodiment will be described with reference to the drawings. FIG. 5 is an exploded perspective view schematically showing the liquid ejection head 200 according to the present embodiment. FIG. 6 is a plan view schematically showing the liquid ejection head 200 according to the present embodiment. FIG. 7 is a cross-sectional view taken along line VII-VII of FIG. 6 schematically showing the liquid ejection head 200 according to the present embodiment. In FIGS. 5 to 7, the X-axis, Y-axis, and Z-axis are illustrated as three axes orthogonal to each other. In FIGS. 5 and 7, the piezoelectric element 30 is illustrated in a simplified manner.

[0062] As shown in FIGS. 5 to 7, the liquid ejection head 200 includes, for example, the actuator 100, a nozzle plate 210, a protective substrate 220, a circuit board 230, and a compliance substrate 240. For convenience, in FIG. 6, the illustration of the circuit board 230 is omitted.

[0063] An opening 12 as a pressure generation chamber is formed in the substrate 10 of the actuator 100. The opening 12 is partitioned by a plurality of partition walls 13. The opening 12 has a volume change when the diaphragm 20 is displaced by the piezoelectric element 30.

[0064] On the substrate 10, a first communication passage 14 and a second communication passage 15 are formed. In the illustrated example, the first communication passage 14 and the second communication passage 15 are formed at the +X-axis direction end of the opening 12. The first communication passage 14 is configured such that its opening area becomes smaller by narrowing the +X-axis direction end of the opening 12 from the Y-axis direction. The width of the second communication passage 15 in the Y-axis direction is, for example, the same as the width of the opening 12 in the Y-axis direction. In the +X-axis direction of the second communication passage 15, a third communication passage 16 communicating with the plurality of second communication passages 15 is formed. The third communication passage 16 constitutes a part of the manifold 17. The manifold 17 serves as a common liquid chamber for each opening 12. Thus, on the substrate 10, a supply flow path 18 composed of the first communication passage 14, the second communication passage 15, and the third communication passage 16 and the opening 12 are formed. The substrate 10 is a flow path forming substrate. The supply flow path 18 communicates with the opening 12 and supplies liquid to the opening 12.

[0065] The nozzle plate 210 is provided on one surface of the substrate 10. The material of the nozzle plate 210 is, for example, SUS (Steel Use Stainless). The nozzle plate 210 is joined to the substrate 10 by, for example, an adhesive or a heat welding film. The substrate 10 is provided between the nozzle plate 210 and the diaphragm 20. A plurality of nozzle holes 212 are formed in the nozzle plate 210 along the Y-axis. The nozzle holes 212 communicate with the opening 12 and discharge liquid.

[0066] In the liquid discharge head 200, the diaphragm 20 and the first electrode 32 are displaced due to the deformation of the piezoelectric layer 36 having electromechanical conversion characteristics. A plurality of piezoelectric elements 30 are provided, for example. The number of the piezoelectric elements 30 is not particularly limited.

[0067] The first electrode 32 is configured as an individual electrode independent for each opening 12. The size of the first electrode 32 in the Y-axis direction is, for example, smaller than the size of the opening 12 in the Y-axis direction. The size of the first electrode 32 in the X-axis direction is, for example, larger than the size of the opening 12 in the X-axis direction. In the X-axis direction, both ends of the first electrode 32 are positioned sandwiching both ends of the opening 12. A lead electrode 202 is connected to the -X-axis direction end of the first electrode 32.

[0068] The size of the piezoelectric layer 36 in the Y-axis direction is, for example, larger than the size of the first electrode 32 in the Y-axis direction. The size of the piezoelectric layer 36 in the X-axis direction is, for example, larger than the size of the opening 12 in the X-axis direction. The +X-axis direction end of the first electrode 32 is positioned, for example, between the +X-axis direction end of the piezoelectric layer 36 and the +X-axis direction end of the opening 12. The +X-axis direction end of the first electrode 32 is covered by the piezoelectric layer 36. The -X-axis direction end of the piezoelectric layer 36 is positioned, for example, between the -X-axis direction side end of the first electrode 32 and the -X-axis direction end of the opening 12. The -X-axis direction side end of the first electrode 32 is not covered by the piezoelectric layer 36.

[0069] The second electrode 38 is provided continuously on the piezoelectric layer 36 and the diaphragm 20, for example. In the illustrated example, the second electrode 38 is configured as a common electrode common to a plurality of piezoelectric elements 30.

[0070] The protective substrate 220 is joined to the diaphragm 20 by an adhesive 203. A through hole 222 is provided in the protective substrate 220. In the illustrated example, the through hole 222 penetrates the protective substrate 220 in the Z-axis direction and communicates with the third communication path 16. The through hole 222 and the third communication path 16 constitute a manifold 17 that serves as a common liquid chamber for each opening 12. Further, a through hole 224 that penetrates the protective substrate 220 in the Z-axis direction is formed in the protective substrate 220. The end of the lead electrode 202 is positioned in the through hole 224.

[0071] An opening 226 is formed in the protective substrate 220. The opening 226 is for the piezoelectric element 30 It is a space for not inhibiting the drive. The opening 226 may or may not be sealed.

[0072] The circuit board 230 is provided on the protection board 220. The circuit board 230 includes a semiconductor integrated circuit (Integrated Circuit: IC) for driving the piezoelectric element 30. The circuit board 230 and the lead electrode 202 are electrically connected via the connection wiring 204.

[0073] The compliance board 240 is provided on the protection board 220. The compliance board 240 has a sealing layer 242 provided on the protection board 220 and a fixing plate 244 provided on the sealing layer 242. The sealing layer 242 is a layer for sealing the manifold 17. The sealing layer 242 has, for example, flexibility. A through hole 246 is formed in the fixing plate 244. The through hole 246 penetrates the fixing plate 244 in the Z-axis direction. The through hole 246 is provided at a position overlapping the manifold 17 when viewed from the Z-axis direction.

[0074] 4. Printer Next, the printer according to the present embodiment will be described with reference to the drawings. FIG. 8 is a perspective view schematically showing the printer 300 according to the present embodiment.

[0075] The printer 300 is an inkjet printer. As shown in FIG. 8, the printer 300 includes a head unit 310. The head unit 310 has, for example, a liquid ejection head 200. The number of the liquid ejection heads 200 is not particularly limited. The head unit 310 is detachably provided with cartridges 312 and 314 constituting a supply means. The carriage 316 on which the head unit 310 is mounted is provided so as to be axially movable on a carriage shaft 322 attached to the apparatus main body 320, and ejects the liquid supplied from the liquid supply means.

[0076] Here, the liquid may be a material in the liquid phase state, and liquid-state materials such as sols and gels are also included in the liquid. Further, not only the liquid as a state of the substance, but also materials in which particles of functional materials composed of solids such as pigments and metal particles are dissolved, dispersed, or mixed in a solvent are included in the liquid. Representative examples of the liquid include ink and liquid crystal emulsifiers. The ink shall include general aqueous inks, oil-based inks, and various liquid compositions such as gel inks and hot melt inks.

[0077] In the printer 300, the driving force of the driving motor 330 is transmitted to the carriage 316 via a plurality of gears (not shown) and a timing belt 332. Thereby, the carriage 316 on which the head unit 310 is mounted is moved along the carriage shaft 322. On the other hand, the apparatus main body 320 is provided with a transport roller 340 as a transport mechanism for relatively moving a sheet S, which is a recording medium such as paper, with respect to the liquid ejection head 200. The transport mechanism for transporting the sheet S is not limited to transport rollers and may be a belt, a drum, or the like.

[0078] The printer 300 includes a printer controller 350 as a control unit that controls the liquid ejection head 200 and the transport roller 340. The printer controller 350 is electrically connected to the circuit board 250 of the liquid ejection head 200. The printer controller 350 includes, for example, a RAM (Random Access Memory) that temporarily stores various data, a ROM (Read Only Memory) that stores control programs, etc., a CPU (Central Processing Unit), and a drive signal generation circuit that generates a drive signal for supplying to the liquid ejection head 200.

[0079] 5. Examples and Comparative Examples 5.1. Preparation of Samples 5.1.1. Example 1 By thermally oxidizing the surface of a single-crystalline silicon substrate, a SiO2 layer with a thickness of 1460 nm was formed. Next, a Zr film with a thickness of 400 nm was deposited by DC (Direct Current) sputtering, and a ZrO2 layer was formed by heat treatment at 850 °C. Thereby, a diaphragm composed of a SiO2 layer and a ZrO2 layer was formed.

[0080] Next, as the first electrode, a Ti layer, a Pt layer, and an Ir layer with thicknesses of 20 nm, 80 nm, and 5 nm, respectively, were formed by DC sputtering.

[0081] Next, a seed layer was formed. Specifically, using bismuth acetate, iron acetate, and titanium tetra-i-propoxide, a precursor solution of BFT was prepared so that the molar ratio of Bi / Fe / Ti = 110 / 50 / 50. The precursor solution was spin-coated to form a film with a thickness of 20 nm, and a BFT crystal layer was obtained by lamp annealing in an oxygen atmosphere at 650 °C for 3 minutes.

[0082] Next, a piezoelectric layer was formed. Specifically, using potassium 2-ethylhexanoate, sodium 2-ethylhexanoate, and niobium 2-ethylhexanoate, a precursor solution of KNN was prepared so that the molar ratio of K / Na / Nb = 52 / 52 / 100. Further, a solution containing manganese 2-ethylhexanoate was used so as to contain 0.2 wt% of MnO as an additive. Such a precursor solution was spin-coated to form a film with a thickness of 70 nm, and a KNN crystal layer was obtained by lamp annealing in an oxygen atmosphere at 700 °C for 3 minutes. Thereafter, the KNN crystal layer was cooled at 5 °C / second using air cooling and water cooling with circulating cooling water. The above process was repeated 12 times to form a piezoelectric layer with a thickness of 840 nm.

[0083] Next, as the second electrode, a Pt layer with a thickness of 50 nm was formed by DC sputtering.

[0084] Next, the second electrode, the piezoelectric layer, and the seed layer were patterned by ion milling to fabricate a piezoelectric element.

[0085] Next, the back surface of the single-crystalline silicon substrate was ground and polished to a thickness of about 400 μm. Next, a chromium oxide layer with a thickness of 60 nm and a chromium layer with a thickness of 100 nm were formed on the polished surface. Next, the chromium oxide layer and the chromium layer were patterned by a wet etching method. Further, the single-crystalline silicon was patterned by a wet etching method to form an opening.

[0086] Thus, the actuator of Example 1 was formed.

[0087] 5.1.2. Example 2 By thermally oxidizing the surface of the single-crystalline silicon substrate, an SiO2 layer with a thickness of 1870 nm was formed as a diaphragm. Next, as the first electrode, a Pt layer with a thickness of 200 nm was formed by DC sputtering.

[0088] Next, using a KNN target prepared to have a molar ratio of K / Na / Nb = 35 / 65 / 100, a piezoelectric layer with a thickness of 1000 nm was formed by RF sputtering.

[0089] Next, as the second electrode, a Pt layer with a thickness of 100 nm was formed by DC sputtering.

[0090] The subsequent steps were the same as those in Example 1.

[0091] Thus, the actuator of Example 2 was formed.

[0092] 5.1.3. Comparative Example 1 By thermally oxidizing the surface of the single-crystalline silicon substrate, an SiO2 layer with a thickness of 1460 nm was formed. Next, Zr with a thickness of 400 nm was deposited by DC sputtering, and a ZrO2 layer was formed by heat treatment at 850 °C. Thus, a diaphragm composed of an SiO2 layer and a ZrO2 layer was formed.

[0093] Next, as the first electrode, Ti layers, Pt layers, Ir layers, and Ti layers with thicknesses of 20 nm, 80 nm, 5 nm, and 4 nm, respectively, were formed by DC sputtering.

[0094] Next, a piezoelectric layer was formed. Specifically, a precursor solution of PZT was prepared so as to have a molar ratio of Pb / Zr / Ti = 118 / 52 / 48 using lead acetate, zirconium butoxide, and titanium tetra-i-propoxide. The precursor solution was formed into a film by the spin coating method, and a PZT crystal film was obtained by lamp annealing in a nitrogen atmosphere at 737 °C for 5 minutes. The above process was repeated 6 times to form a piezoelectric layer with a thickness of 1200 nm.

[0095] Next, a second electrode was formed. Specifically, an Ir layer and a Ti layer with thicknesses of 5 nm and 4 nm, respectively, were formed by DC sputtering. Next, lamp annealing was performed in a nitrogen atmosphere at 740 °C for 8 minutes to form an Ir layer and a Ti layer with thicknesses of 6 nm and 25 nm, respectively.

[0096] The subsequent steps were the same as those in Example 1.

[0097] Thus, the actuator of Comparative Example 1 was formed.

[0098] 5.2. Experimental Method 5.2.1. Spontaneous Polarization and Remnant Polarization As the measuring device, a ferroelectric tester FCE manufactured by Toyo Technica Co., Ltd. and a voltage amplifier F10A manufactured by Toyo Technica Co., Ltd. were used. A triangular wave with a frequency of 66 Hz and an electric field of 290 kV / cm was applied to the piezoelectric layer with an area of 97680 μm 2 in plan view to obtain a hysteresis curve. Fitting was performed using a modified Miller model obtained by modifying the model by Miller to calculate the spontaneous polarization and the remnant polarization. The modified Miller model is shown in the following formulas (1) to (3).

[0099]

Equation

[0100] In formulas (1) to (3), P is the polarization amount, Ps is the spontaneous polarization, Pr is the remanent polarization, V is the voltage, Vc is the coercive voltage, Vm is the maximum applied voltage, and Pm is the polarization amount when Vm is applied.

[0101] 5.2.2. Displacement As a measuring device for the displacement of the diaphragm, an arbitrary waveform generator AFG3022C manufactured by Tektronix, a voltage amplifier HSA4011 manufactured by NF Circuit Design Block Co., Ltd., an oscilloscope HDO4024 manufactured by Teledyne Lecroy, and a laser displacement meter NLV-2500 manufactured by Polytec were used. A square wave with a voltage width of 5V to 35V output from the arbitrary waveform generator and amplified 10 times by the voltage amplifier was applied to the piezoelectric layer having the same area as above. Then, the displacement of the diaphragm was detected by the laser displacement meter, the displacement was converted into a voltage and captured by the oscilloscope. The minimum voltage was adjusted so that the displacement was maximized in Examples 1 and 2 and Comparative Example 1. The decrease rate of the displacement when the electric field was reduced by 10% and the increase rate of the displacement when the electric field was increased by 10% were evaluated around 210 kV / cm, and the value obtained by dividing the latter by the former was used as an evaluation index for the linearity of the hysteresis curve (hereinafter also referred to as "linearity"). It can be said that the closer this index is to 1, the higher the linearity.

[0102] 5.2.3. Tensile stress Using a thin film stress measurement device FLX-2908 (manufactured by KLA-Tencor), the tensile stress of the piezoelectric layers of Examples 1 and 2 and Comparative Example 1 was determined from the warpage amount of the laminated sample.

[0103] Specifically, on a silicon substrate with a diameter of 150 mm, except for the range with an outer circumference of 1 mm, each layer was laminated as described in "Fabrication of Samples" above, and the warpage amounts of the laminated samples before and after forming the piezoelectric thin layer were measured. Specifically, the warpage amount was measured for the shape of the range excluding the range with an outer circumference of 10 mm on the straight line including the center of the laminated sample. In the cases of Examples 1 and 2 and Comparative Example 1, since the center is concave, the difference in height in the direction perpendicular to the sample surface between both ends of the straight line and the center is the warpage amount.

[0104] When the amount of warpage is sufficiently shorter than 130 mm, which is the range in which the shape was measured, the stress in the piezoelectric layer is obtained by the following formula (4).

[0105] [Number]

[0106] In formula (4), σ is the tensile stress, E S is the Young's modulus of the substrate, v is the Poisson's ratio of the substrate, L is the length of the measurement range, t S is the thickness of the substrate, t F is the thickness of the piezoelectric layer, z B is the amount of warpage of the laminated sample after formation of the piezoelectric layer, z A is the amount of warpage of the laminated sample after formation of the piezoelectric layer.

[0107] 5.2.4. Lattice constant In Example 1 and Comparative Example 1, the lattice constants of the piezoelectric layer and the underlayer were measured. The underlayer is the layer immediately below the piezoelectric layer, which is the BFT layer in Example 1 and the Pt layer in Comparative Example 1. Using a thin film X-ray diffractometer (D8 Discover, manufactured by Bruker AXS), the X-ray diffraction peaks of the crystal were obtained by the normal 2θ-ω method using Cu-Kα rays, and the lattice constant was obtained from Bragg's formula.

[0108] 5.3. Experimental results Figure 9 is the hysteresis curve of Example 1. Figure 10 is the hysteresis curve of Example 2. Figure 11 is the hysteresis curve of Comparative Example 1. In Figures 9 to 11, the measured values are shown by thick lines and the fitting data are shown by thin lines.

[0109] Figure 12 is a graph showing the relationship between the electric field generated in the piezoelectric layer and the displacement amount of the diaphragm in Examples 1 and 2 and Comparative Example 2. The vertical axis in Figure 12 is the displacement amount normalized with the displacement amount of the diaphragm at an electric field of 210 kV / cm as "1".

[0110] ​Figure 13 is a table showing a list of experimental results of Examples 1 and 2 and Comparative Example 1. For "spontaneous polarization" and "residual polarization" in Figure 13, the value read from Figures 9 to 11 is supplemented with the tolerance of "±0.2". "Residual polarization / spontaneous polarization" indicates the range considering the tolerance.

[0111] As shown in Figure 13, Examples 1 and 2 had higher linearity compared to Comparative Example 1. It was found that by making the residual polarization 0.535 times or less of the spontaneous polarization, the linearity could be made 0.94 or more.

[0112] At low voltages, since the amount of polarization is small, the diaphragm is mainly displaced by the electrostriction of the piezoelectric layer. Since the displacement amount due to electrostriction is proportional to the square of the voltage, the greater the voltage, the greater the increase in the external force applied to the diaphragm by the piezoelectric layer. This is offset by the resistance due to the increase in the displacement amount of the diaphragm, and it is considered that the linearity of the hysteresis curve of the entire actuator system is improved.

[0113] As shown in Figure 13, in Example 1, the lattice constant of the piezoelectric layer was smaller than that of the underlying layer. On the other hand, in Comparative Example 1, the lattice constant of the piezoelectric layer was larger than that of the underlying layer. In Example 1, a strong tensile stress was generated in the piezoelectric layer compared to Comparative Example 1.

[0114] The above-described embodiments and modifications are examples and are not limited thereto. For example, it is also possible to appropriately combine each embodiment and each modification.

[0115] The present invention includes a configuration that is substantially the same as the configuration described in the embodiment, for example, a configuration having the same functions, methods, and results, or a configuration having the same objectives and effects. The present invention also includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. The present invention also includes a configuration that exhibits the same operating effects as the configuration described in the embodiment or a configuration that can achieve the same objective. The present invention also includes a configuration in which known techniques are added to the configuration described in the embodiment.

[0116] The following content is derived from the above-described embodiments and modifications.

[0117] One aspect of the actuator is a diaphragm, a first electrode provided above the diaphragm, a piezoelectric layer provided above the first electrode and containing a complex oxide having a perovskite structure, a second electrode provided above the piezoelectric layer, and includes the remanent polarization of the piezoelectric layer is 0.535 times or less of the spontaneous polarization of the piezoelectric layer.

[0118] According to this actuator, even if the applied voltage between the first electrode and the second electrode is increased, an increase in the displacement amount of the diaphragm can be suppressed from becoming small.

[0119] In one aspect of the actuator, the remanent polarization is 12.2 μC / cm 2 or less, and the spontaneous polarization may be 23.2 μC / cm 2 or less.

[0120] According to this actuator, the remanent polarization can be made 0.535 times or less of the spontaneous polarization.

[0121] In one aspect of the actuator, when the electric field generated in the piezoelectric layer is increased by 10% from 210 kV / cm, the increase rate of the displacement amount of the diaphragm may be 0.94 or more with respect to the decrease rate of the displacement amount of the diaphragm when the electric field is decreased by 10% from 210 kV / cm.

[0122] According to this actuator, the linearity of the hysteresis curve can be enhanced.

[0123] In one aspect of the actuator, the tensile stress of the piezoelectric layer may be 261 MPa or more.

[0124] According to this actuator, the residual polarization can be reduced, and the linearity of the hysteresis curve can be enhanced.

[0125] In one aspect of the actuator, including a seed layer provided between the first electrode and the piezoelectric layer, the lattice constant of the piezoelectric layer in the in-plane direction may be smaller than the lattice constant of the seed layer in the in-plane direction.

[0126] According to this actuator, a tensile stress can be generated in the piezoelectric layer.

[0127] One aspect of the liquid ejection head is one aspect of the actuator, and a nozzle plate in which nozzle holes are formed, and the substrate is provided between the nozzle plate and the diaphragm, and a pressure generation chamber communicating with the nozzle holes is formed.

[0128] One aspect of the printer is the liquid ejection head, and a conveyance mechanism that relatively moves a recording medium with respect to the liquid ejection head, and a control unit that controls the liquid ejection head and the conveyance mechanism. and

Explanation of Reference Numerals

[0129] 10… Substrate, 12… Opening, 13… Partition wall, 14… First communication path, 15… Second communication path, 16… Third communication path, 17… Manifold, 18… Supply flow path, 20… Diaphragm, 22… First layer, 24… Second layer, 30… Piezoelectric element, 32… First electrode, 34… Seed layer, 36… Piezoelectric layer, 36a… Crystal structure, 38… Second electrode, 100… Actuator, 200… Liquid ejection head, 202… Lead electrode, 203… Adhesive, 204… Connection wiring, 210… Nozzle plate, 212… Nozzle hole, 220… Protection substrate, 222, 224… Through hole, 226… Opening, 230… Circuit board, 240… Compliance substrate, 242… Sealing layer, 244… Fixing plate, 246… Through hole, 300… Printer, 310… Head unit, 312, 314… Cartridge, 316… Carriage, 320… Device body, 330… Driving motor, 332… Timing belt, 340… Conveyor roller, 350… Printer controller

Claims

1. A diaphragm, A first electrode provided above the diaphragm, A piezoelectric layer provided above the first electrode and containing a complex oxide with a perovskite structure, A second electrode provided above the piezoelectric layer, comprising An actuator, wherein the remanent polarization of the piezoelectric layer is 0.535 times or less of the spontaneous polarization of the piezoelectric layer.

2. In Claim 1, the remanent polarization is 12.2 μC / cm ２ or less, and the spontaneous polarization is 23.2 μC / cm ２ or less. An actuator.

3. In Claim 1, when the electric field generated in the piezoelectric layer is increased by 10% from 210 kV / cm, the increase rate of the displacement amount of the diaphragm is 0.94 or more with respect to the decrease rate of the displacement amount of the diaphragm when the electric field is decreased by 10% from 210 kV / cm. An actuator.

4. In Claim 1, the tensile stress of the piezoelectric layer is 261 MPa or more. An actuator.

5. In Claim 1, including a seed layer provided between the first electrode and the piezoelectric layer, and the lattice constant of the piezoelectric layer in the in-plane direction is smaller than the lattice constant of the seed layer in the in-plane direction. An actuator.

6. An actuator according to any one of Claims 1 to 5, a flow path forming substrate in which a pressure generating chamber whose volume changes by the actuator is formed, and a nozzle plate provided with nozzle holes communicating with the pressure generating chamber, including a liquid ejection head.

7. The liquid ejection head according to claim 6, A transport mechanism that relatively moves a recording medium with respect to the liquid ejection head, A control unit that controls the liquid ejection head and the transport mechanism, A printer comprising the same.

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