Piezoelectric element, liquid discharge head, and printer

Abstract

To provide a piezoelectric element that has a large absolute value of a piezoelectric constant and can prevent a variation in piezoelectric characteristics due to an imprint phenomenon.SOLUTION: A piezoelectric element includes a first electrode and a second electrode, and a piezoelectric layer that is provided between the first electrode and the second electrode and has a perovskite structure. When a positive predetermined voltage is applied to the piezoelectric layer, the voltage applied to the piezoelectric layer is reduced to 0 V, and after the lapse of 0.1 seconds, a voltage waveform of a triangular wave whose maximum voltage is the predetermined voltage is applied to the piezoelectric layer to obtain a hysteresis curve that is drawn counterclockwise, and when the amount of remanent polarization of a starting point of the hysteresis curve is P1 and the amount of remanent polarization of an end point of the hysteresis curve is P2, the relationships of 0<P1 / P2≤0.5 and 0<P1 are satisfied.SELECTED DRAWING: Figure 12

Description

Technical Field

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

Background Art

[0002] Currently, piezoelectric elements are used in various fields such as liquid ejection heads and sensors of inkjet printers. As the piezoelectric body, for example, potassium sodium niobate and lead zirconate titanate are used. Such a piezoelectric body is known to have a remanent polarization.

[0003] For example, Patent Document 1 describes that in order to obtain high characteristics in a piezoelectric element, it is necessary to increase the remanent polarization.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in a piezoelectric element having a large remanent polarization, the piezoelectric characteristics may vary due to an imprint phenomenon in which an offset voltage is applied in the piezoelectric layer.

Means for Solving the Problems

[0006] One aspect of the piezoelectric element according to the present invention is a first electrode and a second electrode, a piezoelectric layer provided between the first electrode and the second electrode and having a perovskite structure, and After applying a positive predetermined voltage to the piezoelectric layer, waiting for 0.1 seconds with the applied voltage to the piezoelectric layer set to 0V, and then applying a voltage waveform of a triangular wave with the maximum voltage being the predetermined voltage to the piezoelectric layer to obtain a hysteresis curve drawn counterclockwise, assuming that the amount of residual polarization at the starting point of the hysteresis curve is P1 and the amount of residual polarization at the ending point of the hysteresis curve is P2, 0 < P1 / P2 ≤ 0.5 and 0 < P1 satisfy the relationship.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

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Figure 4

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Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Embodiments for Carrying Out the Invention

[0008] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. Note 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 constituent elements of the present invention.

[0009] 1. Piezoelectric element 1.1. Configuration First, the piezoelectric element according to the present embodiment will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing the piezoelectric element 100 according to the present embodiment.

[0010] As shown in FIG. 1, the piezoelectric element 100 includes a first electrode 10, a piezoelectric layer 20, and a second electrode 30. The piezoelectric element 100 is provided on a substrate 2.

[0011] The substrate 2 is, for example, a flat plate formed of a semiconductor, an insulator, or the like. The substrate 2 may be a single layer or a laminate in which a plurality of layers are laminated. The substrate 2 is not limited in its internal structure as long as its upper surface has a planar shape, and may have a structure in which a space or the like is formed inside.

[0012] The substrate 2 may have flexibility and include a diaphragm that deforms by the operation of the piezoelectric layer 20. The diaphragm is, for example, a silicon oxide layer, a zirconium oxide layer, or a laminate in which a zirconium oxide layer is provided on a silicon oxide layer.

[0013] The first electrode 10 is provided on the substrate 2. The first electrode 10 is provided between the substrate 2 and the piezoelectric layer 20. The shape of the first electrode 10 is, for example, layer-like. The thickness of the first electrode 10 is, for example, 3 nm or more and 300 nm or less. The first electrode 10 is, for example, a metal layer such as a platinum layer, an iridium layer, a titanium layer, a ruthenium layer, their conductive oxide layers, a lanthanum nickelate (LaNiO3: LNO) layer, a strontium ruthenium oxide (SrRuO3 : SRO) layer, etc. The first electrode 10 may have a structure in which a plurality of the layers exemplified above are laminated.

[0014] The first electrode 10 is one of the electrodes for applying a voltage to the piezoelectric layer 20. The first electrode 10 is a lower electrode provided under the piezoelectric layer 20.

[0015] The piezoelectric layer 20 is provided on the first electrode 10. The piezoelectric layer 20 is provided between the first electrode 10 and the second electrode 30. Although not shown, the piezoelectric layer 20 may be provided on the first electrode 10 and on the substrate 2. The thickness of the piezoelectric layer 20 is, for example, 100 nm or more and 3 μm or less. The piezoelectric layer 20 can be deformed when a voltage is applied between the first electrode 10 and the second electrode 30.

[0016] The piezoelectric layer 20 has a perovskite structure. The piezoelectric layer 20 is, for example, a KNN layer containing potassium (K), sodium (Na), and niobium (Nb). In the piezoelectric layer 20, the atomic concentration D of the B-site B with respect to the atomic concentration D of the A-site A ratio D A / D B is, for example, 1.01 or more and 1.10 or less, preferably 1.02 or more and 1.06 or less. For example, when the piezoelectric layer 20 is a KNN layer, in the piezoelectric layer 20, the total number of potassium atoms and sodium atoms is, for example, 1% or more and 10% or less, preferably 2% or more and 6% or less more than the number of niobium atoms.

[0017] The second electrode 30 is provided on the piezoelectric layer 20. Although not shown, if the second electrode 30 is electrically separated from the first electrode 10, it may be further provided on the side surface of the piezoelectric layer 20 and on the substrate 2.

[0018] The shape of the second electrode 30 is, for example, layered. The thickness of the second electrode 30 is, for example, 3 nm or more and 300 nm or less. The second electrode 30 is, for example, a metal layer such as an iridium layer, a platinum layer, a titanium layer, a ruthenium layer, their conductive oxide layers, a lanthanum nickelate layer, a strontium ruthenate layer, etc. The second electrode 30 may have a structure in which a plurality of the layers exemplified above are laminated.

[0019] The second electrode 30 is the other electrode for applying a voltage to the piezoelectric layer 20. The second electrode 30 is an upper electrode provided on the piezoelectric layer 20.

[0020] 1.2. Hysteresis Curve FIG. 2 is a graph for explaining the voltage applied to the piezoelectric layer 20 to obtain a hysteresis curve. FIG. 3 is a hysteresis curve of the piezoelectric element 100 obtained by the voltage waveform shown in FIG. 2.

[0021] To obtain the hysteresis curve shown in FIG. 3, first, as shown in FIG. 2, a positive predetermined voltage is applied to the piezoelectric layer 20 for a predetermined period (step S1). Specifically, the predetermined period is 1 millisecond. In the example shown in FIG. 2, +30 V is applied. Here, the "positive voltage" means a voltage at which the first electrode 10 is positive with respect to the second electrode 30. The "negative voltage" means a voltage at which the first electrode 10 is negative with respect to the second electrode 30.

[0022] Next, the applied voltage to the piezoelectric layer 20 is set to 0 V and 0.1 second elapses (step S2).

[0023] Next, a triangular voltage waveform is applied to the piezoelectric layer 20 to obtain a hysteresis curve (step S3). The triangular wave is a waveform that draws a hysteresis curve counterclockwise. That is, as shown in FIG. 2, the triangular wave has a waveform of 0V, a negative voltage, 0V, a positive voltage, and 0V. In the illustrated example, the starting point of the triangular wave is T1 and the ending point of the triangular wave is T2. The applied voltage at the starting point T1 and the ending point T2 is 0V. The maximum positive voltage applied to the piezoelectric layer 20 by the triangular wave is the predetermined voltage applied in step S1. In the illustrated example, the maximum positive voltage is +30V. The absolute value of the maximum negative voltage applied to the piezoelectric layer 20 by the triangular wave is the same as the absolute value of the maximum positive voltage. In the illustrated example, the maximum negative voltage is -30V.

[0024] As shown in FIG. 3, assuming that the remanent polarization amount at the starting point T1 of the hysteresis curve is P1 and the remanent polarization amount at the ending point T2 of the hysteresis curve is P2, the piezoelectric element 100 satisfies the relationship of the following formula (1).

[0025] 0 < P1 / P2 ≦ 0.5, and 0 < P1 ···(1)

[0026] As described above, the piezoelectric layer 20 has a perovskite structure, and the atomic concentration D of the B site B with respect to the atomic concentration D of the A site A of the ratio D A / D B is 1.01 or more and 1.10 or less, preferably 1.02 or more and 1.06 or less. Thus, by making the piezoelectric layer 20 have a composition that is not a chemical amphoteric composition of the perovskite structure, the piezoelectric layer 20 has defects. Since a part of the remanent polarization is lost due to the leakage current caused by this defect, the piezoelectric element 100 can satisfy the formula (1).

[0027] Note that the method of forming defects in the piezoelectric layer 20 is not limited to the method of setting the ratio D A / D B within the above range Not determined. For example, when the piezoelectric layer 20 is a KNN layer, defects may be formed by removing potassium atoms or sodium atoms in the crystal lattice from the crystal lattice by heat treatment. Thereby, a hysteresis curve satisfying the formula (1) can be obtained.

[0028] Alternatively, impurities may be introduced into the piezoelectric layer 20, and a part of the remanent polarization may be lost due to the leakage current caused by the introduced impurities. Thereby, the piezoelectric element 100 may satisfy the formula (1). The introduction of impurities may be performed by substituting an element with a different valence for the A site or B site of the perovskite structure, or may be performed by adding a light element that easily moves in the layer. When the piezoelectric layer 20 is a KNN layer, examples of the element with a different valence include Ca with a valence of +2 with respect to K and Na with a valence of +1, and Ti with a valence of +4 with respect to Nb with a valence of +5. Examples of the light element that easily moves include K, Na, B, and Li.

[0029] Alternatively, by introducing space charges that cancel the polarization into the piezoelectric layer 20, the piezoelectric element 100 may satisfy the formula (1).

[0030] 1.3. Operational effects In the piezoelectric element 100, when a positive predetermined voltage is applied to the piezoelectric layer 20, after the applied voltage to the piezoelectric layer 20 is set to 0 V and 0.1 seconds have elapsed, a voltage waveform of a triangular wave whose maximum voltage is the predetermined voltage is applied to the piezoelectric layer 20 and a hysteresis curve drawn counterclockwise is obtained, if the remanent polarization amount at the starting point T1 of the hysteresis curve is P1 and the remanent polarization amount at the ending point T2 of the hysteresis curve is P2, then 0 < P1 / P2 ≤ 0.5 and 0 < P1 are satisfied.

[0031] As described above, since the piezoelectric element 100 has P1 / P2 ≤ 0.5, it is possible to suppress the imprint phenomenon in which an offset voltage is applied to the piezoelectric layer as compared with the case where P1 / P2 is greater than 0.5. The offset voltage gradually increases over time because the magnitude of the remanent polarization accumulates with the holding time or the number of holding times. Therefore, the piezoelectric characteristics fluctuate, which becomes a reliability problem.

[0032] Furthermore, in the piezoelectric element 100, since 0 < P1 / P2, the absolute value of the piezoelectric constant is larger than when P1 / P2 is zero or less. If P1 / P2 is zero or less, the polarization state becomes unclear. Therefore, for example, when driving the piezoelectric element by applying a positive voltage, electrical energy is used to determine the polarization direction, which results in loss and leads to a delay in driving and a degradation of piezoelectric characteristics.

[0033] As described above, by satisfying 0 < P1 / P2 ≤ 0.5 and P1 > 0, the piezoelectric element 100 can have a large absolute value of the piezoelectric constant and suppress fluctuations in piezoelectric characteristics due to the imprint phenomenon.

[0034] 2. Method for manufacturing piezoelectric element Next, a method for manufacturing the piezoelectric element 100 according to the present embodiment will be described with reference to the drawings.

[0035] As shown in FIG. 1, a substrate 2 is prepared. Specifically, a silicon oxide layer is formed by thermally oxidizing a silicon substrate. Next, a zirconium layer is formed on the silicon oxide layer by a sputtering method or the like, and a zirconium oxide layer is formed by thermally oxidizing the zirconium layer. Thereby, a diaphragm composed of a silicon oxide layer and a zirconium oxide layer can be formed. The substrate 2 can be prepared by the above steps.

[0036] Next, a first electrode 10 is formed on the substrate 2. The first electrode 10 is formed, for example, by a sputtering method or a vacuum evaporation method. Next, the first electrode 10 is patterned. The patterning is performed, for example, by photolithography and etching.

[0037] Next, a piezoelectric layer 20 is formed on the first electrode 10. The piezoelectric layer 20 is formed by a CSD (Chemical Solution Deposition) method such as the sol-gel method or MOD (Metal Organic Deposition). Hereinafter, the method for forming the piezoelectric layer 20 will be described.

[0038] First, for example, a metal complex containing potassium, a metal complex containing sodium, and a metal complex containing niobium are dissolved or dispersed in an organic solvent to prepare a precursor solution.

[0039] Examples of the metal complex containing potassium include potassium 2-ethylhexanoate and potassium acetate. Examples of the metal complex containing sodium include sodium 2-ethylhexanoate and sodium acetate. Examples of the metal complex containing niobium include niobium 2-ethylhexanoate, niobium ethoxide, pentaethoxynbium, and pentabutoxynbium. Note that two or more metal complexes may be used in combination. For example, as the metal complex containing potassium, potassium 2-ethylhexanoate and potassium acetate may be used in combination.

[0040] Examples of the solvent 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, 2-n-ethylhexane, or a mixed solvent thereof.

[0041] Next, the prepared precursor solution is applied onto the first electrode 10 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 fired at, for example, 550°C or higher and 800°C or lower to be crystallized, thereby forming a crystal layer.

[0042] Then, a series of steps from the application of the above precursor solution to the firing of the precursor layer are repeated multiple times. Thereby, a piezoelectric layer 20 composed of a plurality of crystal layers can be formed. Next, the piezoelectric layer 20 is patterned. The patterning is performed, for example, by photolithography and etching. Note that a piezoelectric layer 20 composed of a single crystal layer may be formed without repeating the series of steps from the application of the precursor solution to the firing of the precursor layer multiple times.

[0043] 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, an RTA (Rapid Thermal Annealing) device.

[0044] Next, a second electrode 30 is formed on the piezoelectric layer 20. The second electrode 30 is formed, for example, by sputtering or vacuum evaporation. Next, the second electrode 30 is patterned. The patterning is performed, for example, by photolithography and etching.

[0045] Through the above steps, the piezoelectric element 100 can be manufactured.

[0046] Note that the patterning of the second electrode 30 and the patterning of the piezoelectric layer 20 may be performed in the same step. Further, when the piezoelectric layer 20 is composed of a plurality of crystal layers, the first crystal layer of the piezoelectric layer 20 and the first electrode 10 may be patterned in the same step.

[0047] 3. Liquid ejection head Next, the liquid ejection head according to the present embodiment will be described with reference to the drawings. FIG. 4 is an exploded perspective view schematically showing the liquid ejection head 200 according to the present embodiment. FIG. 5 is a plan view schematically showing the liquid ejection head 200 according to the present embodiment. FIG. 6 is a cross-sectional view taken along line VI-VI of FIG. 5 schematically showing the liquid ejection head 200 according to the present embodiment. In FIGS. 4 to 6, the X-axis, Y-axis, and Z-axis are illustrated as three axes orthogonal to each other. In addition, in FIGS. 4 and 6, the piezoelectric element 100 is shown in a simplified manner.

[0048] As shown in FIGS. 4 to 6, the liquid ejection head 200 includes, for example, a substrate 2, a piezoelectric element 100, a nozzle plate 220, a protective substrate 240, a circuit board 250, and a compliance substrate 260. The substrate 2 has a flow path forming substrate 210 and a diaphragm 230. For the sake of convenience, in FIG. 5, the illustration of the circuit board 250 is omitted.

[0049] The flow path forming substrate 210 is, for example, a silicon substrate. A pressure generating chamber 211 is provided in the flow path forming substrate 210. The pressure generating chamber 211 is partitioned by a plurality of partition walls 212. The volume of the pressure generating chamber 211 changes due to the piezoelectric element 100.

[0050] A first communication path 213 and a second communication path 214 are provided at the +X-axis direction end of the pressure generating chamber 211 of the flow path forming substrate 210. The first communication path 213 is configured such that its opening area becomes smaller by narrowing the +X-axis direction end of the pressure generating chamber 211 from the Y-axis direction. The width of the second communication path 214 in the Y-axis direction is, for example, the same as the width of the pressure generating chamber 211 in the Y-axis direction. A third communication path 215 that communicates with the plurality of second communication paths 214 is provided in the +X-axis direction of the second communication path 214. The third communication path 215 constitutes a part of the manifold 216. The manifold 216 serves as a common liquid chamber for each pressure generating chamber 211. In this way, the flow path forming substrate 210 is provided with a supply flow path 217 including the first communication path 213, the second communication path 214, and the third communication path 215, and the pressure generating chamber 211. The supply flow path 217 communicates with the pressure generating chamber 211 and supplies liquid to the pressure generating chamber 211.

[0051] The nozzle plate 220 is provided on one side surface of the flow path forming substrate 210. The material of the nozzle plate 220 is, for example, SUS (Steel Use Stainless). The nozzle plate 220 is joined to the flow path forming substrate 210 by, for example, an adhesive or a thermal welding film. A plurality of nozzle holes 222 are provided in the nozzle plate 220 along the Y-axis. The nozzle holes 222 communicate with the pressure generating chamber 211 and discharge the liquid.

[0052] The diaphragm 230 is provided on the other side surface of the flow path forming substrate 210. The diaphragm 230 is composed of, for example, a silicon oxide layer 232 provided on the flow path forming substrate 210 and a zirconium oxide layer 234 provided on the silicon oxide layer 232.

[0053] The piezoelectric element 100 is provided, for example, on the diaphragm 230. A plurality of piezoelectric elements 100 are provided. The number of the piezoelectric elements 100 is not particularly limited.

[0054] In the liquid discharge head 200, the diaphragm 230 and the first electrode 10 are displaced by the deformation of the piezoelectric layer 20 having electromechanical conversion characteristics. That is, in the liquid discharge head 200, the diaphragm 230 and the first electrode 10 substantially function as a diaphragm.

[0055] The first electrode 10 is configured as an individual electrode independent for each pressure generating chamber 211. The width of the first electrode 10 in the Y-axis direction is narrower than the width of the pressure generating chamber 211 in the Y-axis direction. The length of the first electrode 10 in the X-axis direction is longer than the length of the pressure generating chamber 211 in the X-axis direction. In the X-axis direction, both ends of the first electrode 10 are positioned sandwiching both ends of the pressure generating chamber 211. A lead electrode 202 is connected to the -X-axis direction end of the first electrode 10.

[0056] The width of the piezoelectric layer 20 in the Y-axis direction is, for example, wider than the width of the first electrode 10 in the Y-axis direction. The length of the piezoelectric layer 20 in the X-axis direction is, for example, longer than the length of the pressure generation chamber 211 in the X-axis direction. The +X-axis end of the first electrode 10 is, for example, located between the +X-axis end of the piezoelectric layer 20 and the +X-axis end of the pressure generation chamber 211. The +X-axis end of the first electrode 10 is covered by the piezoelectric layer 20. On the other hand, the -X-axis end of the piezoelectric layer 20 is, for example, located between the -X-axis side end of the first electrode 10 and the +X-axis end of the pressure generation chamber 211. The -X-axis side end of the first electrode 10 is not covered by the piezoelectric layer 20.

[0057] The second electrode 30 is, for example, continuously provided on the piezoelectric layer 20 and the diaphragm 230. The second electrode 30 is configured as a common electrode shared by the plurality of piezoelectric elements 100.

[0058] The protective substrate 240 is joined to the diaphragm 230 by an adhesive 203. The protective substrate 240 is provided with a through hole 242. In the illustrated example, the through hole 242 penetrates the protective substrate 240 in the Z-axis direction and communicates with the third communication path 215. The through hole 242 and the third communication path 215 constitute a manifold 216 that serves as a common liquid chamber for each pressure generation chamber 211. Further, the protective substrate 240 is provided with a through hole 244 that penetrates the protective substrate 240 in the Z-axis direction. The end of the lead electrode 202 is located in the through hole 244.

[0059] The protective substrate 240 is provided with an opening 246. The opening 246 is a space for not inhibiting the driving of the piezoelectric element 100. The opening 246 may or may not be sealed.

[0060] The circuit board 250 is provided on the protective substrate 240. The circuit board 250 includes a semiconductor integrated circuit (IC) for driving the piezoelectric element 100. The circuit board 250 and the lead electrode 202 are electrically connected via a connection wiring 204.

[0061] The compliance substrate 260 is provided on the protection substrate 240. The compliance substrate 260 has a sealing layer 262 provided on the protection substrate 240 and a fixing plate 264 provided on the sealing layer 262. The sealing layer 262 is a layer for sealing the manifold 216. The sealing layer 262 has, for example, flexibility. The fixing plate 264 is provided with a through hole 266. The through hole 266 penetrates the fixing plate 264 in the Z-axis direction. The through hole 266 is provided at a position overlapping the manifold 216 when viewed from the Z-axis direction.

[0062] 4. Printer Next, the printer according to the present embodiment will be described with reference to the drawings. FIG. 7 is a perspective view schematically showing the printer 300 according to the present embodiment.

[0063] The printer 300 is an inkjet printer. As shown in FIG. 7, 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. A 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.

[0064] Here, the liquid may be a material in a liquid phase state, and liquid state materials such as sols and gels are also included in the liquid. Further, not only the liquid as one state of the substance, but also those in which particles of a functional material 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.

[0065] In the printer 300, the driving force of the drive motor 330 is transmitted to the carriage 316 via a plurality of gears (not shown) and a timing belt 332, so that the carriage 316 equipped with the head unit 310 is moved along the carriage shaft 322. On the other hand, in the apparatus main body 320, a conveyance roller 340 is provided as a conveyance mechanism for relatively moving a sheet S, which is a recording medium such as paper, with respect to the liquid ejection head 200. The conveyance mechanism for conveying the sheet S is not limited to the conveyance roller, and may be a belt, a drum, or the like.

[0066] The printer 300 includes a printer controller 350 as a control unit for controlling the liquid ejection head 200 and the conveyance 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) for temporarily storing various data, a ROM (Read Only Memory) storing a control program and the like, a CPU (Central Processing Unit), and a drive signal generation circuit for generating a drive signal for supplying to the liquid ejection head 200.

[0067] Note that the piezoelectric element 100 can be used in a wide range of applications, not limited to liquid ejection heads and printers. The piezoelectric element 100 is preferably used as a piezoelectric actuator such as an ultrasonic motor, a vibration type dust removing device, a piezoelectric transformer, a piezoelectric speaker, a piezoelectric pump, a pressure-electric conversion device, etc. Further, the piezoelectric element 100 is preferably used as a piezoelectric type sensor element such as an ultrasonic detector, an angular velocity sensor, an acceleration sensor, a vibration sensor, an inclination sensor, a pressure sensor, a collision sensor, a human sensor, an infrared sensor, a terahertz sensor, a heat detection sensor, a pyroelectric sensor, a piezoelectric sensor, etc. Further, the piezoelectric element 100 is preferably used as a ferroelectric element such as a ferroelectric memory (FeRAM), a ferroelectric transistor (FeFET), a ferroelectric arithmetic circuit (FeLogic), a ferroelectric capacitor, etc. Further, the piezoelectric element 100 is preferably used as a voltage control type optical element such as a wavelength converter, an optical waveguide, an optical path modulator, a refractive index control element, an electronic shutter mechanism, etc.

[0068] 5. Examples and Comparative Examples 5.1. Preparation of Samples 5.1.1. Example 1 In Example 1, first, the surface of a single crystal silicon substrate was thermally oxidized to form a SiO2 layer having a thickness of 1460 nm. Next, a Zr layer having a thickness of 400 nm was formed by DC (Direct Current) sputtering method, and a ZrO2 layer was formed by heat treatment at 850 °C. On top of that, Ti layer and Pt layer having thicknesses of 20 nm and 80 nm respectively were formed by DC sputtering method.

[0069] Next, the surface of the Pt layer was irradiated with ultraviolet rays in a vacuum for 10 minutes, and then exposed to a nitrogen atmosphere for 1 minute to clean the surface of the Pt layer. Then, a KNN precursor solution was spin-coated to form a 70-nm film, and a KNN layer was formed by lamp annealing in an oxygen atmosphere at 750°C for 3 minutes. The KNN precursor solution was adjusted so that (K+Na):Nb = 104:100 and K:Na = 50:50. Next, the layer above the ZrO2 layer was patterned by ion milling. Next, a KNN precursor solution with the same composition as above was spin-coated in 11 layers to form a total film thickness of 400 nm. Lamp annealing was performed on each layer in an oxygen atmosphere at 750°C for 3 minutes to crystallize the KNN layer.

[0070] Next, a 45-nm Pt layer was formed by DC sputtering. In plan view, the diameter of the second electrode was 500 μm.

[0071] 5.1.2. Example 2 In Example 2, a KNN layer with (K+Na):Nb = 104:100 and K:Na = 35:65 was formed to a thickness of 1 μm by sputtering, and the rest was fabricated in the same manner as in Example 1.

[0072] 5.1.3. Comparative Example 1 In Comparative Example 1, a KNN precursor solution was adjusted so that (K+Na):Nb = 100:100 and K:Na = 35:65, and the rest was fabricated in the same manner as in Example 1.

[0073] 5.1.4. Comparative Example 2 In Comparative Example 2, in the same manner as in Example 1, after forming the Ti layer, Pt layer, Ir layer, and Ti layer, the PZT precursor solution was spin-coated to form a film with a thickness of 110 nm, and the PZT layer was formed by lamp annealing in an oxygen atmosphere at 737 °C for 5 minutes. The PZT precursor solution was adjusted so that Pb:Zr:Ti = 118:52:48. Next, the layer above the ZrO2 layer was patterned by ion milling. Next, the ZPT precursor solution with the same composition as above was spin-coated in 5 layers to form a film with a total thickness of 1085 nm. Lamp annealing was performed on each layer in an oxygen atmosphere at 737 °C for 5 minutes to crystallize the PZT layer.

[0074] Next, Ir layers and Ti layers 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. Thereafter, the PZT layer, Ir layer, and Ti were patterned by ion milling. Next, Ir layers and Ti layers with thicknesses of 6 nm and 25 nm, respectively, were formed and patterned by ion milling.

[0075] 5.2. Evaluation in Hysteresis Curve As shown in Figure 2, a positive predetermined voltage at which each sample is sufficiently polarized was applied to the piezoelectric layer for 1 millisecond. After the applied voltage to the piezoelectric layer was set to 0 V and 0.1 second had elapsed, a triangular wave voltage waveform of 0 V, negative voltage, 0 V, positive voltage, 0 V was applied to the piezoelectric layer. Thereby, a hysteresis curve was obtained.

[0076] Figure 8 is the hysteresis curve of Example 1. Figure 9 is the hysteresis curve of Example 2. Figure 10 is the hysteresis curve of Comparative Example 1. Figure 11 is the hysteresis curve of Comparative Example 2. Figure 12 is a table showing the evaluation results obtained by plotting the values in Figures 8 to 11.

[0077] In FIG. 12, the residual polarization amount P1 at the starting point T1 of the hysteresis curve, the residual polarization amount P2 at the ending point T2 of the hysteresis curve, and P1 / P2 are shown. Further, in FIG. 12, for each sample, after applying a positive predetermined voltage to the piezoelectric layer, the residual polarization amount P3 at the starting point T1 of the hysteresis curve obtained when the period during which no voltage is applied to the piezoelectric layer is set to 1 second instead of 0.1 second is shown.

[0078] Furthermore, in FIG. 12, the piezoelectric constant d 31 is shown. In the measurement of the piezoelectric constant, first, each sample was cut out into a strip shape with a length of 15 mm and a width of 4 mm in a plan view, and a cantilever beam with one end fixed was fabricated. Then, a sine-wave voltage waveform of 0 V, a positive voltage, and 0 V was continuously applied to one electrode, and the movement amounts (displacement amounts) of the fixed end and the opposite end were measured with a laser, and the piezoelectric constant d was obtained by calculation. 31

[0079] Furthermore, in FIG. 12, the leakage current after 60 seconds when an electric field of 200 kV / cm is applied to each sample at room temperature is shown.

[0080] As shown in FIG. 12, in Comparative Example 1 where P1 / P2 is negative, the absolute value of the piezoelectric constant was smaller than that in Examples 1 and 2 where P1 / P2 is a positive value. In Comparative Example 1, since P1 / P2 is negative, the effect of the polarization treatment (poling) is lost, and when driving the piezoelectric element by applying a positive voltage, electrical energy is used to determine the polarization direction, and that part becomes a loss, resulting in a smaller absolute value of the piezoelectric constant.

[0081] Also, as shown in FIG. 12, in Examples 1 and 2, the leakage current was smaller than that in Comparative Examples 1 and 2. P1 / P2 is considered to depend on the magnitude of the leakage current, and P1 / P2 can be controlled by adjusting the leakage current. Also, no significant difference was confirmed between P1 and P3.

[0082] ​FIG. 13 is a graph showing the variation of (Pm - Pr) when a unipolar square pulse of 50 kHz is continuously applied at each operating voltage in Example 1 and Comparative Example 2. Pm is the polarization amount when a positive maximum voltage is applied. Pr is the residual polarization amount. The difference between Pm and Pr (Pm - Pr) is said to be a measure of the variation in the operation of the piezoelectric element. The horizontal axis of FIG. 13 is the number of square pulses. The vertical axis of FIG. 13 is the value normalized by the initial value of (Pm - Pr).

[0083] As shown in FIG. 13, in the case of 10 billion pulses, in Comparative Example 2, characteristic variations of about 15% were observed, whereas in Example 1, the characteristic variations could be suppressed to about 10%. In Comparative Example 2, as shown in FIG. 12, since P1 / P2 is 0.5 or more and the residual polarization amount is large, it is considered that the influence of the imprint phenomenon is large.

[0084] From the above, it was found that by satisfying 0 < P1 / P2 ≤ 0.5 and P1 > 0, the absolute value of the piezoelectric constant is large and the variation in piezoelectric characteristics due to the imprint phenomenon can be suppressed.

[0085] The present invention is not limited to the above-described embodiments, and various modifications are further possible. For example, the present invention includes a configuration that is substantially the same as the configuration described in the embodiments. Substantially the same configuration means, for example, a configuration having the same functions, methods, and results, or a configuration having the same objectives and effects. Further, the present invention includes a configuration in which a non-essential part of the configuration described in the embodiments is replaced. Further, the present invention includes a configuration having the same operating effects as the configuration described in the embodiments or a configuration capable of achieving the same objective. Further, the present invention includes a configuration in which a known technique is added to the configuration described in the embodiments.

[0086] The following contents are derived from the above-described embodiments.

[0087] One aspect of the piezoelectric element is a first electrode and a second electrode, and A piezoelectric layer having a perovskite structure, provided between the first electrode and the second electrode; comprising; When a positive predetermined voltage is applied to the piezoelectric layer, and after allowing 0.1 seconds to elapse with the applied voltage to the piezoelectric layer set to 0V, a voltage waveform of a triangular wave having a maximum voltage of the predetermined voltage is applied to the piezoelectric layer to obtain a hysteresis curve drawn counterclockwise, assuming that the amount of remnant polarization at the starting point of the hysteresis curve is P1 and the amount of remnant polarization at the ending point of the hysteresis curve is P2, 0 < P1 / P2 ≦ 0.5 and 0 < P1 satisfies the relationship.

[0088] According to this piezoelectric element, the absolute value of the piezoelectric constant is large, and fluctuations in piezoelectric characteristics due to the imprint phenomenon can be suppressed.

[0089] In one aspect of the piezoelectric element, the piezoelectric layer may contain potassium, sodium, and niobium.

[0090] One aspect of a liquid ejection head is one aspect of the piezoelectric element, a flow path forming substrate provided with a pressure generating chamber whose volume changes by the piezoelectric element, a nozzle plate provided with nozzle holes communicating with the pressure generating chamber, and comprising.

[0091] One aspect of a printer is one aspect of the liquid ejection head, a conveyance mechanism for relatively moving a recording medium with respect to the liquid ejection head, a control unit for controlling the liquid ejection head and the conveyance mechanism, and comprising.

Explanation of Reference Numerals

[0092] 2 … Substrate, 10 … First electrode, 20 … Piezoelectric layer, 30 … Second electrode, 100 … Piezoelectric element, 200 … Liquid ejection head, 202 … Lead electrode, 203 … Adhesive, 204 … Connection wiring, 210 … Flow path forming substrate, 211 … Pressure generating chamber, 212 … Partition wall, 213 … First communication path, 214 … Second communication path, 215 … Third communication path, 216 … Manifold, 217 … Supply flow path, 220 … Nozzle plate, 222 … Nozzle hole, 230 … Diaphragm, 232 … Silicon oxide layer, 234 … Zirconium oxide layer, 240 … Protection substrate, 242, 244 … Through hole, 246 … Opening, 250 … Circuit board, 260 … Compliance substrate, 262 … Sealing layer, 264 … Fixing plate, 266 … Through hole, 300 … Printer, 310 … Head unit, 312, 314 … Cartridge, 316 … Carriage, 320 … Apparatus main body, 322 … Carriage shaft, 330 … Drive motor, 332 … Timing belt, 340 … Conveyor roller, 350 … Printer controller

Claims

1. a first electrode and a second electrode; a piezoelectric layer provided between the first electrode and the second electrode and having a perovskite structure; comprising when a positive predetermined voltage is applied to the piezoelectric layer, the applied voltage to the piezoelectric layer is set to 0 V and after 0.1 second has elapsed, a voltage waveform of a triangular wave having a maximum voltage of the predetermined voltage is applied to the piezoelectric layer to obtain a hysteresis curve drawn counterclockwise, when the residual polarization amount at the start point of the hysteresis curve is P1 and the residual polarization amount at the end point of the hysteresis curve is P2, a piezoelectric element satisfying the relationship of 0 < P1 / P2 ≤ 0.5 and 0 < P1 .

2. The piezoelectric element according to claim 1, wherein the piezoelectric layer contains potassium, sodium, and niobium.

3. the piezoelectric element according to claim 1 or 2; a flow path forming substrate provided with a pressure generating chamber whose volume changes by the piezoelectric element; a nozzle plate provided with nozzle holes communicating with the pressure generating chamber; a liquid ejection head comprising.

4. the liquid ejection head according to claim 3; a conveyance mechanism for relatively moving a recording medium with respect to the liquid ejection head; a control unit for controlling the liquid ejection head and the conveyance mechanism; a printer comprising.

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