Piezoelectric element and liquid ejection head

Abstract

Provided is a piezoelectric element and a liquid ejection head that maintain good piezoelectric characteristics while suppressing leakage current. The piezoelectric element includes: a first electrode; an oxide layer formed on the first electrode; a piezoelectric layer formed on the oxide layer and containing potassium, sodium, and niobium; and a second electrode formed on the piezoelectric layer, wherein when a potential difference of 10 V is applied between the first electrode and the second electrode, the current density of the leakage current differs by 10,000 times or more when the first electrode is at a high potential and when the second electrode is at a high potential.

Description

Technical Field

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

[0002] Piezoelectric elements are used in various fields such as liquid ejection heads or sensors of inkjet printers. As the piezoelectric body, for example, sodium potassium niobate or lead zirconate titanate is used. The piezoelectric element operates by disposing the piezoelectric body between a pair of electrodes and applying an electric field to the piezoelectric body by the electrodes. In such a piezoelectric element, a leakage current that does not contribute to the operation sometimes occurs.

[0003] For example, in Patent Document 1, in order to suppress the leakage current of the piezoelectric element, some elements of the piezoelectric body are replaced.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2014-112675

[0007] However, although the leakage current tends to be suppressed by the method of replacing elements of the piezoelectric body, it is rather likely to cause dielectric breakdown and may impair the piezoelectric characteristics. Therefore, a piezoelectric element that maintains good piezoelectric characteristics while suppressing the leakage current is required. Summary of the Invention

[0008] One aspect of the piezoelectric element according to the present invention includes:

[0009] a first electrode;

[0010] an oxide layer formed on the first electrode;

[0011] a piezoelectric body layer formed on the oxide layer and containing potassium, sodium, and niobium; and

[0012] a second electrode formed on the piezoelectric body layer,

[0013] wherein when a potential difference of 10 V is applied between the first electrode and the second electrode, the current density of the leakage current differs by 10,000 times or more in the case where the first electrode is at a high potential and in the case where the second electrode is at a high potential.

[0014] One aspect of the liquid ejection head according to the present invention includes:

[0015] the above piezoelectric element;

[0016] a flow path forming substrate provided with a pressure generating chamber whose volume changes by the piezoelectric element; and

[0017] The nozzle plate is provided with nozzle holes communicating with the pressure generating chamber. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a cross-sectional view schematically showing the piezoelectric element according to the present embodiment.

[0019] Figure 2 is an exploded perspective view schematically showing the liquid ejector according to the present embodiment.

[0020] Figure 3 is a top view schematically showing the liquid ejector according to the present embodiment.

[0021] Figure 4 is a cross-sectional view schematically showing the liquid ejector according to the present embodiment.

[0022] Figure 5 is a perspective view schematically showing the printer according to the present embodiment.

[0023] Figure 6 are the measurement results of the leakage current of the examples and comparative examples.

[0024] Figure 7 are the evaluation results of the displacement amounts of the examples and comparative examples.

[0025] REFERENCE SIGNS

[0026] 2, substrate; 10, first electrode; 20, oxide layer; 30, piezoelectric layer; 40, second electrode; 100, piezoelectric element; 200, liquid ejector; 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, protective substrate; 242, 244, through hole; 246, opening; 250, circuit board; 260, flexible substrate; 262, sealing layer; 264, fixing plate; 266, through hole; 300, printer; 310, head unit; 312, 314, ink cartridge; 316, carriage; 320, apparatus main body; 322, carriage shaft; 330, drive motor; 332, timing belt; 340, conveying roller; 350, printer controller. DETAILED DESCRIPTION OF THE INVENTION

[0027] Next, embodiments of the present invention will be described. The embodiments described below illustrate examples of the present invention. The present invention is in no way limited to the following embodiments and also includes various modified forms implemented within the scope of not changing the gist of the present invention. It should be noted that not all of the configurations described below are necessarily essential configurations of the present invention.

[0028] 1. Piezoelectric element

[0029] The piezoelectric element according to this embodiment includes: a first electrode; an oxide layer formed on the first electrode; a piezoelectric layer formed on the oxide layer and containing potassium, sodium, and niobium; and a second electrode formed on the piezoelectric layer.

[0030] 1.1. Configuration

[0031] First, the piezoelectric element according to this embodiment will be described with reference to the accompanying drawings. Figure 1 It is a cross-sectional view schematically showing the piezoelectric element 100 according to this embodiment.

[0032] As Figure 1 shown, the piezoelectric element 100 includes a first electrode 10, an oxide layer 20, a piezoelectric layer 30, and a second electrode 40. The piezoelectric element 100 is provided on a substrate 2.

[0033] 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 formed by laminating multiple layers. The substrate 2 only needs to have a planar shape on its upper surface, and the internal structure is not limited and may be a structure with a space formed inside, for example. The substrate 2 may be, for example, a silicon substrate. In this case, the silicon substrate is more preferably a silicon substrate preferentially oriented in the (100) plane. In this way, the piezoelectric element can be more suitably used as a configuration of a liquid ejection head with low leakage current and high efficiency.

[0034] The substrate 2 may also include a diaphragm that has flexibility and deforms by the operation of the piezoelectric layer 30. The diaphragm is, for example, a silicon oxide layer, a zirconium oxide layer, or a laminate such as a zirconium oxide layer provided on a silicon oxide layer.

[0035] The first electrode 10 is provided on the substrate 2. The first electrode 10 is provided between the substrate 2 and the oxide layer 20. The shape of the first electrode 10 is, for example, a layer shape. 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, or the like, and may also be a conductive oxide layer thereof as long as sufficient conductivity can be obtained. The first electrode 10 may also have a structure formed by laminating multiple layers exemplified above.

[0036] The first electrode 10 is an electrode for applying a voltage to the piezoelectric layer 30. The first electrode 10 is a lower electrode disposed below when viewed from the piezoelectric layer 30.

[0037] The oxide layer 20 is disposed on the first electrode 10. The oxide layer 20 is disposed between the first electrode 10 and the piezoelectric layer 30. It should be noted that although not shown, the oxide layer 20 may also be disposed on at least one of the first electrode 10 and the substrate 2. The thickness of the oxide layer 20 is, for example, 5 nm or more and 50 nm or less, preferably 10 nm or more and 40 nm or less, and more preferably 20 nm or more and 30 nm or less. As described later, a pn junction is formed at the boundary between the oxide layer 20 and the piezoelectric layer 30. Therefore, unlike the conductive oxide layer included as a candidate for the first electrode 10 described above, the oxide layer 20 is preferably crystallized, and more preferably has a consistent orientation in the direction perpendicular to the surface of the first electrode 10.

[0038] The material of the oxide layer 20 is not particularly limited as long as it can form a pn junction with the material of the piezoelectric layer 30. For example, oxides containing strontium and ruthenium, oxides containing lanthanum and nickel, and oxides containing strontium and titanium can be exemplified. These oxides may also be doped with additives as needed. As additives, for example, niobium, lanthanum, etc. can be listed, and they can be appropriately selected considering the valence, etc., so as to be able to form a pn junction. When doping additives, it can be carried out by the same method as semiconductor manufacturing, or by mixing the raw materials for formation.

[0039] The material of the oxide layer 20 more preferably contains strontium and ruthenium. In this way, a pn junction can be formed without doping. It should be noted that even for a material containing strontium and ruthenium, the electrical properties can be adjusted by doping or the like.

[0040] The piezoelectric layer 30 is disposed on the oxide layer 20. The piezoelectric layer 30 is disposed between the first electrode 10 and the second electrode 40. It should be noted that although not shown, the piezoelectric layer 30 may also be disposed on the first electrode 10, on the oxide layer 20, and / or on the substrate 2. The thickness of the piezoelectric layer 30 is, for example, 100 nm or more and 3 μm or less. By applying a voltage between the first electrode 10 and the second electrode 40, the piezoelectric layer 30 can be deformed.

[0041] The piezoelectric layer 30 has a perovskite structure. The piezoelectric layer 30 contains potassium (K), sodium (Na), and niobium (Nb). In this article, a material containing potassium (K), sodium (Na), and niobium (Nb) is sometimes referred to as KNN. In the piezoelectric layer 30, the atomic concentration D of the A-site of the perovskite structure A relative to the atomic concentration D of the B-site B ratio D A / D BFor example, it is 1.01 or more and 1.10 or less, preferably 1.02 or more and 1.06 or less. When the piezoelectric layer 30 is KNN, in the piezoelectric layer 30, the total number of potassium atoms and sodium atoms is more than the number of niobium atoms by, for example, 1% or more and 10% or less, preferably more than 2% or more and 6% or less.

[0042] The second electrode 40 is disposed on the piezoelectric layer 30. It should be noted that although not shown, as long as the second electrode 40 is electrically separated from the first electrode 10, it may also be disposed on the side surface of the piezoelectric layer 30 and the substrate 2.

[0043] The shape of the second electrode 40 is, for example, a layer shape. The thickness of the second electrode 40 is, for example, 3 nm or more and 300 nm or less. The second electrode 40 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 40 may also have a structure in which a plurality of the above-exemplified layers are stacked.

[0044] The second electrode 40 is another electrode for applying a voltage to the piezoelectric layer 30. The second electrode 40 is an upper electrode disposed on the piezoelectric layer 30.

[0045] 1.2. Regarding leakage current

[0046] In the development of KNN thin films for the purpose of suppressing leakage current, generally, the lattice defects of the complex oxide crystals in the piezoelectric layer are reduced, and the number of carriers is minimized as much as possible. The KNN thin films developed according to such a policy tend to have a reduced leakage current. However, although this KNN thin film functions when a low voltage (small potential difference) is applied, when a high voltage (large potential difference) is applied, insulation breakdown sometimes occurs.

[0047] The main reason for the insulation breakdown of this KNN thin film is considered to be due to the concentration of charges in the defects. When a potential difference (voltage) stress is applied to this KNN thin film with fewer defects, charges are likely to concentrate in each defect in this KNN thin film. Therefore, even when a relatively low voltage is applied, a leakage path is formed in this KNN thin film via the defects. Therefore, the voltage range that can be applied to the piezoelectric element is limited, and the degree of freedom in the design and development of devices using the piezoelectric element is limited.

[0048] The piezoelectric layer 30 of the piezoelectric element 100 of the present embodiment forms a pn junction at the boundary with the oxide layer 20 on the first electrode 10. The piezoelectric layer 30 of the present embodiment originally has a relatively large number of carriers as a whole. Therefore, charges are difficult to concentrate in specific defects. As a result, there is a large margin for free movement of charges in the piezoelectric layer 30. According to this mechanism, it is considered that the piezoelectric element of the present embodiment is likely to suppress the concentration of charges under the stress of applied voltage.

[0049] In the piezoelectric element 100 of the present embodiment, as described above, a pn junction is formed at the boundary between the piezoelectric layer 30 and the oxide layer 20. That is, the piezoelectric element 100 has electrical properties similar to those of a diode. Compared with the current flowing into the piezoelectric layer 30 to which a voltage (potential difference) reverse-biased with respect to the pn junction is applied, the current flowing into the piezoelectric layer 30 to which a voltage (potential difference) forward-biased with respect to the pn junction is applied is higher. Therefore, by making the current flowing into the piezoelectric layer 30 reverse-biased with respect to the pn junction, leakage current can be suppressed. Further, as described above, the entire piezoelectric layer 30 of the piezoelectric element 100 of the present embodiment has a large number of carriers, so even when a voltage (potential difference) reverse-biased with respect to the pn junction is applied, dielectric breakdown is difficult to occur.

[0050] Therefore, in the piezoelectric element 100 of the present embodiment, when a potential difference of 10 V is applied between the first electrode 10 and the second electrode 40, the current density of the leakage current differs by more than 10,000 times between the case where the first electrode 10 is at a high potential and the case where the second electrode 40 is at a high potential. The difference in the current density of the leakage current is more preferably more than 150,000 times, and further preferably more than 200,000 times. If the difference in the current density is within the above range, the piezoelectric element 100 to which a current is applied in a specific polarity has a more significant effect of suppressing leakage current than a piezoelectric element in which a pn junction is not formed at the boundary between the piezoelectric layer and the oxide layer. On the other hand, the difference in the current density may be more than 50,000 times or more than 10,000 times. Even if the difference in the current density is within the above range, the piezoelectric element 100 to which a current is applied in a specific polarity sufficiently obtains the effect of suppressing leakage current compared with a piezoelectric element in which a pn junction is not formed at the boundary between the piezoelectric layer and the oxide layer.

[0051] In the pn junction of the piezoelectric element 100 of the present embodiment, the piezoelectric layer 30 is KNN and forms a p-type region. And the oxide layer 20 is formed of a material that will become an n-type region. Therefore, the piezoelectric element 100 is driven under a reverse bias in which the potential of the first electrode 10 is higher than the potential of the second electrode 40.

[0052] 1.3. Deformation of the piezoelectric element

[0053] As the piezoelectric element of the present embodiment, as long as a piezoelectric layer containing potassium, sodium, and niobium is disposed between a pair of electrodes, an oxide layer is disposed between one electrode and the piezoelectric layer, and a pn junction is formed at the boundary between the piezoelectric layer and the oxide layer. And when driving the piezoelectric element, it is driven in such a way that a reverse bias voltage is applied with respect to the pn junction. Therefore, the substrate can be disposed on any one of the electrodes, and as long as a drive signal is applied according to the reverse bias, the above excellent effects can be obtained.

[0054] For example, in the piezoelectric element 100 described above, the first electrode 10 is in contact with the substrate 2, and the first electrode 10 is disposed between the substrate 2 and the oxide layer 20. However, in the piezoelectric element, the second electrode 40 may be in contact with the substrate 2, and the second electrode 40 may be disposed between the substrate 2 and the piezoelectric layer 30.

[0055] Furthermore, there may be two or more pn junctions formed between a pair of electrodes. For example, in the piezoelectric element, a piezoelectric layer containing potassium, sodium, and niobium may be disposed between a pair of electrodes, an oxide layer may be disposed between one electrode and the piezoelectric layer, an oxide layer may be disposed between the other electrode and the piezoelectric layer, and pn junctions may be respectively formed at the boundaries between the two piezoelectric layers and the oxide layers. Even in this case, the same effect can be obtained by applying a drive signal in a reverse bias manner with respect to at least one pn junction.

[0056] The piezoelectric element may also be constituted by including a plurality of piezoelectric elements 100. Each piezoelectric element 100 is disposed between a common electrode and a discrete electrode. The common electrode may be either the first electrode 10 or the second electrode 40 of each piezoelectric element 100. When the piezoelectric element has a common electrode, a voltage that is reverse-biased with respect to the pn junction is also applied to the piezoelectric element 100.

[0057] In addition, when the potential of the common electrode of each piezoelectric element 100 is the reference potential, it is more preferable that the potential of the discrete electrode is lower than the potential of the common electrode. In this way, when a plurality of piezoelectric elements 100 are arranged and disposed, the drive signal sent to one piezoelectric element 100 is less likely to be affected by the drive signal sent to another piezoelectric element 100, the noise is reduced, and more stable operation can be performed.

[0058] 2. Manufacturing method of piezoelectric element

[0059] Next, a manufacturing method of the piezoelectric element 100 according to the present embodiment will be described with reference to the drawings.

[0060] As Figure 1 shown, the 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. Thus, a diaphragm composed of a silicon oxide layer and a zirconium oxide layer can be formed. The substrate 2 can be prepared through the above steps.

[0061] Next, the 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.

[0062] Next, an oxide layer 20 is formed on the first electrode 10. The oxide layer 20 is formed, for example, by a sputtering method or a vacuum evaporation method. Next, the oxide layer 20 is patterned. The patterning is performed, for example, by photolithography and etching. The oxide layer 20 can also be formed by a CSD (Chemical Solution Deposition) method such as a sol-gel method or a MOD (Metal Organic Deposition). In addition, the oxide layer 20 can be formed before patterning the first electrode 10, and then the oxide layer 20 is patterned together with the first electrode 10.

[0063] Next, a piezoelectric layer 30 is formed on the oxide layer 20. The piezoelectric layer 30 is formed by a CSD (Chemical Solution Deposition) method such as a sol-gel method or a MOD (Metal Organic Deposition). Hereinafter, the formation method of the piezoelectric layer 30 will be described.

[0064] First, a metal complex containing potassium, a metal complex containing sodium, and a metal complex containing niobium are dissolved or dispersed in an organic solvent, for example, to prepare a precursor solution.

[0065] 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, pentaethoxyniobium, and pentabutoxyniobium. It should be noted that two or more metal complexes can also be used in combination. For example, as the metal complex containing potassium, potassium 2-ethylhexanoate and potassium acetate can be used in combination.

[0066] Examples of the solvent include propanol, butanol, pentanol, hexanol, octanol, ethylene glycol, propylene glycol, octane, decane, cyclohexane, xylene, toluene, tetrahydrofuran, acetic acid, octanoic acid, 2-n-butoxyethanol, n-octane, 2-n-ethylhexane, or a mixed solvent thereof.

[0067] Next, the prepared precursor solution is coated on the oxide layer 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 time to dry it. Further, the dried precursor layer is heated at, for example, 300°C or higher and 450°C or lower and held for a certain time to perform degreasing. Then, the degreased precursor layer is crystallized by firing at, for example, 550°C or higher and 800°C or lower to form a crystal layer.

[0068] Then, the above series of steps from the coating of the precursor solution to the firing of the precursor layer are repeated multiple times. Thereby, a piezoelectric layer 30 composed of multiple crystal layers can be formed. Next, the piezoelectric layer 30 is patterned. The patterning is performed, for example, by photolithography and etching. It should be noted that the piezoelectric layer 30 composed of a single crystal layer may also be formed without repeating the series of steps from the coating of the precursor solution to the firing of the precursor layer multiple times.

[0069] The heating device used in the drying and degreasing of the precursor layer is, for example, a hot plate. The heating device used in the firing of the precursor layer is, for example, an RTA (Rapid Thermal Annealing) device.

[0070] Next, a second electrode 40 is formed on the piezoelectric layer 30. The second electrode 40 is formed, for example, by sputtering or vacuum evaporation. Next, the second electrode 40 is patterned. The patterning is performed, for example, by photolithography and etching.

[0071] Through the above steps, the piezoelectric element 100 can be manufactured.

[0072] It should be noted that the patterning of the second electrode 40 and the patterning of the piezoelectric layer 30 may also be performed in the same step. In addition, when the piezoelectric layer 30 is composed of multiple crystal layers, the first crystal layer of the piezoelectric layer 30 and the first electrode 10 may also be patterned in the same step. Further, when the piezoelectric layer 30 is composed of multiple crystal layers, the first crystal layer of the piezoelectric layer 30, the first electrode 10, and the oxide layer 20 may also be patterned in the same step.

[0073] 3. Liquid ejection head

[0074] Next, the liquid ejection head according to the present embodiment will be described with reference to the drawings. Figure 2 is a schematic exploded perspective view showing the liquid ejection head 200 according to the present embodiment. Figure 3 is a schematic top view showing the liquid ejection head 200 according to the present embodiment. Figure 4 is a schematic view showing the liquid ejection head 200 according to the present embodiment Figure 3 of the cross-sectional view taken along line VI-VI. It should be noted that in Figures 2 to 4 , the X-axis, Y-axis, and Z-axis are shown as three mutually orthogonal axes. In addition, in Figure 2 and Figure 4 , the piezoelectric element 100 is shown in a simplified manner.

[0075] As Figures 2 to 4As shown, the liquid ejection head 200 includes, for example, a base 2, a piezoelectric element 100, a nozzle plate 220, a protective substrate 240, a circuit substrate 250, and a flexible substrate 260. The base 2 has a flow path forming substrate 210 and a diaphragm 230. It should be noted that, for convenience, in Figure 3 the illustration of the circuit substrate 250 is omitted.

[0076] The flow path forming substrate 210 is, for example, a silicon substrate. A pressure generation chamber 211 is provided on the flow path forming substrate 210. The pressure generation chamber 211 is partitioned by a plurality of partition walls 212. The volume of the pressure generation chamber 211 changes by the piezoelectric element 100.

[0077] A first communication path 213 and a second communication path 214 are provided at the +X-axis direction end of the pressure generation chamber 211 on the flow path forming substrate 210. The first communication path 213 is configured to narrow the +X-axis direction end of the pressure generation chamber 211 in the Y-axis direction, thereby reducing the opening area of the first communication path 213. The width of the second communication path 214 in the Y-axis direction is, for example, the same as the width of the pressure generation chamber 211 in the Y-axis direction. A third communication path 215 communicating with a plurality of second communication paths 214 is provided in the +X-axis direction of the second communication path 214. The third communication path 215 forms a part of a manifold 216. The manifold 216 is a common liquid chamber for each pressure generation chamber 211. Thus, a supply flow path 217 composed of the first communication path 213, the second communication path 214, and the third communication path 215 and the pressure generation chamber 211 are provided on the flow path forming substrate 210. The supply flow path 217 communicates with the pressure generation chamber 211 and supplies liquid to the pressure generation chamber 211.

[0078] The nozzle plate 220 is provided on one surface of the flow path forming substrate 210. The material of the nozzle plate 220 is, for example, SUS (Steel Use Stainless, stainless steel). The nozzle plate 220 is joined to the flow path forming substrate 210 by, for example, an adhesive or a hot melt adhesive film. A plurality of nozzle holes 222 are provided along the Y-axis on the nozzle plate 220. The nozzle holes 222 communicate with the pressure generation chamber 211 and eject liquid.

[0079] The diaphragm 230 is provided on the other 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.

[0080] The piezoelectric element 100 is provided, for example, on the diaphragm 230. A plurality of piezoelectric elements 100 are provided. The number of piezoelectric elements 100 is not particularly limited.

[0081] In the liquid ejection head 200, the diaphragm 230 and the first electrode 10 are displaced by the deformation of the piezoelectric layer 30 having electro-mechanical conversion characteristics. That is, in the liquid ejection head 200, the diaphragm 230 and the first electrode 10 substantially function as a diaphragm.

[0082] The first electrode 10 is configured in the form of discrete electrodes independent for each pressure generation chamber 211. The width of the first electrode 10 in the Y-axis direction is narrower than the width of the pressure generation 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 generation chamber 211 in the X-axis direction. In the X-axis direction, the positions of both ends of the first electrode 10 sandwich both ends of the pressure generation chamber 211. A lead electrode 202 is connected to the end portion of the first electrode 10 in the -X axis direction.

[0083] The oxide layer 20 covers the first electrode 10. Among them, it is preferable that the end portion of the first electrode 10 on the -X axis direction side is not covered by the oxide layer 20. Since the oxide layer 20 is not formed between the lead electrode 202 and the first electrode 10, a decrease in conductivity can be suppressed.

[0084] The width of the piezoelectric layer 30 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 30 in the X-axis direction is, for example, longer than the length of the pressure generation chamber 211 in the X-axis direction. The end portion of the first electrode 10 in the +X axis direction is, for example, located between the end portion of the piezoelectric layer 30 in the +X axis direction and the end portion of the pressure generation chamber 211 in the +X axis direction. The end portion of the first electrode 10 in the +X axis direction is covered by the piezoelectric layer 30. On the other hand, the end portion of the piezoelectric layer 30 in the -X axis direction is, for example, located between the end portion of the first electrode 10 on the -X axis direction side and the end portion of the pressure generation chamber 211 in the +X axis direction. The end portion of the first electrode 10 on the -X axis direction side is not covered by the piezoelectric layer 30.

[0085] The second electrode 40 is continuously provided on the piezoelectric layer 30 and the diaphragm 230, for example. The second electrode 40 is configured as a common electrode shared by a plurality of piezoelectric elements 100.

[0086] The protective substrate 240 is joined to the diaphragm 230 by an adhesive 203. Through holes 242 are provided in the protective substrate 240. In the illustrated example, the through holes 242 penetrate the protective substrate 240 in the Z-axis direction and communicate with the third communication path 215. The through holes 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, through holes 244 that penetrate the protective substrate 240 in the Z-axis direction are provided in the protective substrate 240. The end portion of the lead electrode 202 is located in the through hole 244.

[0087] An opening 246 is provided on the protective substrate 240. The opening 246 is a space that does not obstruct the driving of the piezoelectric element 100. The opening 246 may or may not be sealed.

[0088] A 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.

[0089] A flexible substrate 260 is provided on the protective substrate 240. The flexible substrate 260 has a sealing layer 262 provided on the protective 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 flexibility, for example. A through hole 266 is provided in the fixing plate 264. The through hole 266 penetrates the fixing plate 264 in the Z-axis direction. When viewed from the Z-axis direction, the through hole 266 is provided at a position overlapping the manifold 216.

[0090] 4. Printer

[0091] Next, the printer according to the present embodiment will be described with reference to the drawings. Figure 7 FIG. is a perspective view schematically showing a printer 300 according to the present embodiment.

[0092] The printer 300 is an inkjet printer. As Figure 7 shown, 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 ink cartridges 312 and 314 constituting a supply unit. A carriage 316 carrying the head unit 310 is axially movably provided on a carriage shaft 322 mounted on a device main body 320, and ejects the liquid supplied by a liquid supply unit.

[0093] Herein, the liquid means a material in a liquid phase state, and liquid materials such as sols and gels are also included in the liquid. In addition, not only the liquid as a state of matter, but also substances in which particles of a functional material composed of solid matter such as pigments or metal particles are dissolved, dispersed, or mixed in a solvent are included in the liquid. As a representative example of the liquid, ink or a liquid crystal emulsifier can be cited. The ink includes various liquid compositions such as general aqueous ink, oil-based ink, gel ink, and hot melt ink.

[0094] In printer 300, the driving force of drive motor 330 is transmitted via a plurality of gears (not shown) and timing belt 332 to carriage 316, causing carriage 316 carrying head unit 310 to move along carriage shaft 322. On the other hand, a conveyance roller 340 is provided on device main body 320. Conveyance roller 340 serves as a conveyance mechanism to relatively move sheet S, which is a recording medium such as paper, relative to liquid ejection head 200. The conveyance mechanism for conveying sheet S is not limited to a conveyance roller and may also be a conveyor belt or a drum, etc.

[0095] Printer 300 includes a printer controller 350. Printer controller 350 serves as a control unit to control liquid ejection head 200 and conveyance roller 340. Printer controller 350 is electrically connected to circuit board 250 of liquid ejection head 200. Printer controller 350 includes, for example, a RAM (Random Access Memory) for temporarily storing various data, a ROM (Read Only Memory) for storing control programs, etc., a CPU (Central Processing Unit), and a drive signal generation circuit for generating a drive signal to be supplied to liquid ejection head 200.

[0096] It should be noted that piezoelectric element 100 is not limited to liquid ejection heads and printers and can be used in a wide range of applications. Piezoelectric element 100 is, for example, suitable as a piezoelectric actuator for an ultrasonic motor, a vibration type dust removing device, a piezoelectric transformer, a piezoelectric speaker, a piezoelectric pump, a pressure-electric conversion device, etc. In addition, piezoelectric element 100 is, for example, suitable as a sensor element of a piezoelectric type 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 thermal detection sensor, a pyroelectric sensor, a piezoelectric sensor. In addition, piezoelectric element 100 is suitable as a ferroelectric element such as a ferroelectric memory (FeRAM), a ferroelectric transistor (FeFET), a ferroelectric arithmetic circuit (FeLogic), a ferroelectric capacitor. Further, piezoelectric element 100 is suitable as a voltage-controlled optical element such as a wavelength converter, an optical waveguide, an optical path modulator, a refractive index control element, an electronic shutter mechanism.

[0097] 5. Examples and Comparative Examples

[0098] Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to these examples.

[0099] 5.1. Fabrication of the Thin-Film Piezoelectric Element of the Example

[0100] First, on a single-crystalline silicon substrate with a (100) surface, a zirconia film with a (100) surface is formed by evaporation. Next, a platinum film with a (100) surface is formed on the zirconia film by DC sputtering.

[0101] Next, on the platinum film, an SrRuO3 film with a (100) surface is formed by RF sputtering. Next, on the SrRuO3 film, a piezoelectric layer is formed by a liquid phase method (chemical solution method). Hereinafter, the method for forming the piezoelectric layer will be described.

[0102] First, 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. The prepared precursor solution is coated on the SrRuO3 film by spin coating to form a precursor layer (coating process). Next, the precursor layer is heated at 180 °C for a certain time to dry it (drying process). Further, the dried precursor layer is heated at 395 °C and held for a certain time to perform degreasing (degreasing process). Next, the degreased precursor layer is heated at 750 °C and held at this temperature for three minutes to crystallize it (firing process).

[0103] Through the above processes, a piezoelectric layer is formed on the SrRuO3 film. It should be noted that by repeating the above series of processes from the coating process to the firing process 40 times, a piezoelectric layer with a thickness of 1.2 μm is formed.

[0104] Next, an upper electrode is formed on the piezoelectric layer. The upper electrode is formed, for example, by film formation based on sputtering or vacuum evaporation methods, etc., and patterning based on photolithography and etching.

[0105] 5.2. Fabrication of thin-film piezoelectric elements of comparative examples

[0106] First, the surface of a single-crystalline silicon substrate with a (112) surface is thermally oxidized to form a SiO2 film with a thickness of 1170 nm. Next, a 40-nm-thick Zr film is formed by DC sputtering, and a ZrO2 film is formed by heat treatment at 850 °C. A 50-nm Pt film is formed on it by DC sputtering.

[0107] Next, in the same manner as in the example, a piezoelectric layer is formed by a liquid phase method. The method for forming and patterning the upper electrode is the same as in the example.

[0108] 5.3. Evaluation method for piezoelectric elements

[0109] (1) Evaluation of leakage current

[0110] Apparatus: 4140B (manufactured by Keysight Technologies)

[0111] Condition: 1 - 40 V / 1 V step, 60 sec. delay / step

[0112] (2) Evaluation of piezoelectric properties

[0113] Equipment: NLV - 2500 (manufactured by Polytec), AFB3022C (manufactured by Textronix), HDO4024 (manufactured by Lecroy)

[0114] Condition: 50 Hz, sine wave, V HIGH = 2 - 40 V, V LOW = 0 V (fixed)

[0115] 5.4. Evaluation results

[0116] Figure 6 The measurement results of the leakage current of the piezoelectric elements in the examples and comparative examples are shown. In the examples, when driving with the lower electrode (the first electrode 10) at a positive voltage, the leakage current is about 5 orders of magnitude less than when driving with the upper electrode (the second electrode 40) at a positive voltage, and there is no dielectric breakdown up to 40 V. On the other hand, in the comparative examples, regardless of the polarity of the voltage, a high leakage current of the same degree is formed, and dielectric breakdown occurs at 30 V in all cases.

[0117] From Figure 6 The leakage current is read as follows.

[0118] · When driving with the lower electrode (the first electrode 10) at a positive voltage (+10 V),

[0119] ·· Example = 3×10 -5 A / cm 2

[0120] ·· Comparative example = 4×10 -4 A / cm 2

[0121] · When driving with the upper electrode (the second electrode 40) at a positive voltage (+10 V),

[0122] ·· Example = 2×10 0 A / cm 2

[0123] ·· Comparative example = 8×10 -4 A / cm 2

[0124] From the above results, it can be seen that in the examples, a pn - junction is formed at the boundary between the KNN layer and the SRO layer, indicating that the leakage current is very different under forward bias and reverse bias, and the leakage current under reverse bias is less than that of the comparative examples.

[0125] Figure 7 Shows the evaluation results of the piezoelectric characteristics of the piezoelectric elements involved in the examples and comparative examples. The KNN film of the piezoelectric element of the example shows good piezoelectric characteristics without breakdown up to 40 V. On the other hand, the piezoelectric element of the comparative example suffered dielectric breakdown at 34 V and lost its function.

[0126] The above-described embodiments and modifications are examples and are not limited thereto. For example, the respective embodiments and respective modifications can also be appropriately combined.

[0127] The present invention includes configurations that are substantially the same as those described in the embodiments, for example, configurations having the same functions, methods, and results, or configurations having the same purposes and effects. In addition, the present invention includes configurations in which non-essential parts of the configurations described in the embodiments are replaced. Furthermore, the present invention includes configurations that can achieve the same functions and effects as those of the configurations described in the embodiments or can achieve the same purposes. In addition, the present invention includes configurations in which known technologies are added to the configurations described in the embodiments.

[0128] The following can be derived from the above-described embodiments and modifications.

[0129] The piezoelectric element includes:

[0130] A first electrode;

[0131] An oxide layer formed on the first electrode;

[0132] A piezoelectric layer formed on the oxide layer and containing potassium, sodium, and niobium; and

[0133] A second electrode formed on the piezoelectric layer,

[0134] wherein when a potential difference of 10 V is applied between the first electrode and the second electrode, the current density of the leakage current differs by more than 10,000 times between the case where the first electrode is at a high potential and the case where the second electrode is at a high potential.

[0135] According to this piezoelectric element, a structure similar to a PN junction is formed between the first electrode and the second electrode, and as a result, the leakage current can be suppressed to be small in a specific potential difference direction.

[0136] In the above piezoelectric element,

[0137] The oxide layer may contain strontium and ruthenium.

[0138] According to this piezoelectric element, the leakage current can be further suppressed.

[0139] In the above piezoelectric element,

[0140] The piezoelectric element includes a substrate,

[0141] The first electrode may be disposed between the substrate and the oxide layer.

[0142] According to this piezoelectric element, a force can be applied to a substrate, and it can function as an actuator with, for example, a small leakage current.

[0143] In the above piezoelectric element,

[0144] The substrate may be a silicon substrate preferentially oriented in the (100) plane.

[0145] According to this piezoelectric element, for example, a liquid ejection head with a small leakage current and high efficiency can be formed.

[0146] In the above piezoelectric element,

[0147] A plurality of the piezoelectric elements are included,

[0148] One of the first electrode and the second electrode is a common electrode, and the other is a discrete electrode,

[0149] When driven, when the potential of the common electrode is used as a reference, the potential of the discrete electrode may be lower than the potential of the common electrode.

[0150] According to this piezoelectric element, when the piezoelectric elements are adjacent to each other, a drive signal for one piezoelectric element is less likely to affect a drive signal for another piezoelectric element, noise is reduced, and further stable operation can be performed.

Claims

1. A piezoelectric element, characterized in that, Comprising: A first electrode; An oxide layer formed on the first electrode; A piezoelectric layer formed on the oxide layer and containing potassium, sodium, and niobium; And A second electrode formed on the piezoelectric layer, wherein when a potential difference of 10 V is applied between the first electrode and the second electrode, the current density of the leakage current differs by more than 10,000 times between the case where the first electrode is at a high potential and the case where the second electrode is at a high potential, A pn junction is formed at the boundary between the oxide layer and the piezoelectric layer, when operating by applying an electric field to the piezoelectric layer using the first electrode and the second electrode, a voltage reverse-biased with respect to the pn junction is applied to form the electric field.

2. The piezoelectric element according to claim 1, wherein the oxide layer contains strontium and ruthenium.

3. The piezoelectric element according to claim 1 or 2, wherein the piezoelectric element includes a substrate, the first electrode is disposed between the substrate and the oxide layer.

4. The piezoelectric element according to claim 3, wherein the substrate is a silicon substrate preferentially oriented in the (100) plane.

5. The piezoelectric element according to claim 1, wherein it includes a plurality of the piezoelectric elements, one of the first electrode and the second electrode is a common electrode, and the other is a discrete electrode, when being driven, when taking the potential of the common electrode as a reference, the potential of the discrete electrode is lower than the potential of the common electrode.

6. A liquid ejection head, characterized in that, Comprising: The piezoelectric element according to any one of claims 1 to 5; A flow path forming substrate provided with a pressure generating chamber whose volume changes by the piezoelectric element; And A nozzle plate provided with nozzle holes communicating with the pressure generating chamber.

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