Piezoelectric elements and their applications

Abstract

This invention provides a lead-free piezoelectric element that exhibits excellent piezoelectric properties and superior dielectric breakdown strength. [Solution] A piezoelectric element comprising a piezoelectric ceramic layer mainly composed of an alkali niobate perovskite oxide and an internal electrode mainly composed of Ni, which are alternately stacked, wherein the alkali niobate perovskite oxide contains a first metal element which is at least one of Ni, Cu, and Ag, and the piezoelectric ceramic layer has an inert layer located at the end face in the stacking direction and an active layer located in the interior in the stacking direction, wherein the concentration [mol%] of the first metal element contained in the alkali niobate perovskite oxide in the active layer is higher than the concentration [mol%] of the first metal element contained in the alkali niobate perovskite oxide in the inert layer.

Description

[Technical Field]

[0001] This disclosure relates to piezoelectric elements. [Background technology]

[0002] Multilayer piezoelectric elements have been known for some time. Generally, piezoelectric elements containing lead-containing PZT-based (lead zirconate titanate-based) ceramics are used as such. However, lead can have adverse effects on the environment. For this reason, lead-free multilayer piezoelectric elements have been proposed, for example, as described in Patent Documents 1 and 2. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 5862983 [Patent Document 2] Patent No. 6094682 [Overview of the project] [Problems that the invention aims to solve]

[0004] Piezoelectric elements are desirable to have excellent piezoelectric properties and excellent dielectric breakdown strength. However, the piezoelectric elements described in Patent Documents 1 and 2 had room for improvement in terms of achieving both piezoelectric properties and dielectric breakdown strength. Therefore, there was a need for a lead-free piezoelectric element that had excellent piezoelectric properties and excellent dielectric breakdown strength. [Means for solving the problem]

[0005] This disclosure can be implemented in the following forms:

[0006] (1) According to one embodiment of the present disclosure, a piezoelectric element is provided. This piezoelectric element is characterized in that piezoelectric ceramic layers mainly composed of an alkali niobate perovskite oxide and internal electrodes mainly composed of Ni are alternately stacked, the alkali niobate perovskite oxide contains a first metal element which is at least one of Ni, Cu, and Ag, the piezoelectric ceramic layers have an inert layer located at the end face in the stacking direction and an active layer located inside in the stacking direction, the concentration [mol%] of the first metal element contained in the alkali niobate perovskite oxide in the active layer is higher than the concentration [mol%] of the first metal element contained in the alkali niobate perovskite oxide in the inert layer. According to this embodiment of the piezoelectric element, excellent piezoelectric properties and excellent dielectric breakdown strength are provided.

[0007] (2) In the piezoelectric element described in (1) above, the first metal element may include Ni. With this form of piezoelectric element, the piezoelectric properties and dielectric breakdown strength can be further improved.

[0008] (3) In the piezoelectric element described in (1) or (2) above, in the active layer, the ratio of the first metal element to Nb contained in the alkali niobate perovskite oxide (first metal element [mol%] / Nb [mol%]) is 0.1% or more and 3.0% or less, and in the inert layer, the ratio of the first metal element to Nb contained in the alkali niobate perovskite oxide (first metal element [mol%] / Nb [mol%]) is 0.05% or less. With this form of piezoelectric element, piezoelectric properties and dielectric breakdown strength can be further improved.

[0009] (4) In the piezoelectric element described in any one of (1) to (3) above, the piezoelectric ceramic layer may further contain an oxide comprising at least one of Mn and Ti. This form of piezoelectric element allows for a dense and reliable piezoelectric ceramic layer, and as a result, a decrease in piezoelectric properties can be suppressed.

[0010] (5) In the piezoelectric element according to any one of (1) to (4) above, the alkali niobate perovskite-type oxide may contain at least one of Mn and Ti. According to this form of piezoelectric element, the piezoelectric characteristics and insulation properties are excellent.

[0011] (6) According to another form of the present disclosure, a component including the piezoelectric element according to any one of (1) to (5) above is provided. According to this form of component, the piezoelectric characteristics are excellent and the dielectric breakdown strength is excellent.

[0012] (7) According to another form of the present disclosure, an apparatus including the component according to (6) above is provided. According to this form of apparatus, the piezoelectric characteristics are excellent and the dielectric breakdown strength is excellent.

[0013] (8) According to another form of the present disclosure, in the apparatus according to (7) above, an apparatus that is any one of an actuator, haptics, a buzzer, and an ultrasonic sensor is provided. According to this form of apparatus, the piezoelectric characteristics are excellent and the dielectric breakdown strength is excellent.

[0014] Note that the present disclosure can be realized in various forms, for example, in the form of a method for manufacturing a piezoelectric element, a method for manufacturing a component including such a piezoelectric element, a method for manufacturing an apparatus including such a component, and the like.

Brief Description of the Drawings

[0015] [Figure 1] It is a cross-sectional view schematically showing a schematic configuration of a piezoelectric element. [Figure 2] It is a schematic diagram showing an example of a schematic configuration of an actuator as an apparatus. [Figure 3] It is a cross-sectional view showing an example of a schematic configuration of haptics as an apparatus. [Figure 4] It is a cross-sectional view showing an example of a schematic configuration of a buzzer as an apparatus. [Figure 5]This is a cross-sectional view showing an example of the schematic configuration of an ultrasonic sensor as a device. [Modes for carrying out the invention]

[0016] A. Embodiments: Figure 1 is a schematic cross-sectional view showing the general configuration of a piezoelectric element 100 as one embodiment of the present disclosure. The piezoelectric element 100 of this embodiment is composed of a laminate 90 having a substantially rectangular parallelepiped external shape, with a substantially square shape when viewed from above. For convenience, in the drawings of the present disclosure, the thickness of each layer of the laminate 90 is shown to be thicker than it actually is, and the number of layers is shown to be less than it actually is. The piezoelectric element 100 comprises a piezoelectric ceramic layer 10, a plurality of internal electrodes 20, and a pair of external electrodes 30.

[0017] The piezoelectric ceramic layer 10 mainly contains an alkali niobate perovskite-type oxide. In this disclosure, "main component" means a component that accounts for 50% or more by volume. The piezoelectric ceramic layer 10 is substantially lead-free. A detailed explanation of the material composition of the piezoelectric ceramic layer 10 will be given later. The piezoelectric ceramic layer 10 has an inert layer 12 and an active layer 14. The inert layer 12 and the active layer 14 are formed by laminating and sintering multiple piezoelectric ceramic sheets.

[0018] The inert layer 12 is located on the end face S1 in the stacking direction D1. In this disclosure, "inert layer 12" means a layer of the piezoelectric ceramic layer 10 that is located outside the layers of the internal electrodes 20 at both ends in the stacking direction D1. Therefore, one surface of the inert layer 12 in the stacking direction D1 is in contact with the internal electrodes 20, and the other surface of the inert layer 12 in the stacking direction D1 is not in contact with the internal electrodes 20. The piezoelectric ceramic layer 10 of this embodiment has two inert layers 12 located at both ends in the stacking direction D1, but one of the inert layers 12 may be omitted.

[0019] The active layer 14 is located inside the piezoelectric ceramic layer 10 in the stacking direction D1. The active layer 14 is formed by multiple layers, each layer sandwiched between the internal electrodes 20 in the stacking direction D1. In this disclosure, "active layer 14" refers to the layer of the piezoelectric ceramic layer 10 that is located inside the layers of the internal electrodes 20 at both ends in the stacking direction D1. The active layer 14 is displaced when a voltage is applied.

[0020] Multiple internal electrodes 20 are stacked alternately with each layer of the piezoelectric ceramic layer 10. Each set of internal electrodes 20 includes multiple electrodes 22 connected to one of a pair of external electrodes 30, and multiple electrodes 24 connected to the other of the pair of external electrodes 30. The piezoelectric ceramic layer 10 and the electrodes 22 and 24 of the internal electrodes 20 are stacked in the order of piezoelectric ceramic layer 10, electrode 22, piezoelectric ceramic layer 10, electrode 24, and this structure is repeated according to the number of layers.

[0021] The internal electrode 20 of this embodiment contains Ni (nickel) as its main component. By containing Ni as the main component of the internal electrode 20, it is possible to suppress an increase in the manufacturing cost of the piezoelectric element 100 compared to a configuration in which noble metals such as Pd (palladium) or Pt (platinum) are the main components. In addition to the main component Ni, the internal electrode 20 may also contain one or more other elements such as Ag (silver), Cu (copper), Pd (palladium), or Pt (platinum). The external electrode 30 of this embodiment is formed with Au (gold) as its main component, but it is not limited to Au and may contain metals such as Pt, Ag, Pd, Ni, or Cu as its main component, or it may be formed from an alloy of these, such as an alloy of Ag-Pd (silver-palladium). When a voltage is applied between the pair of external electrodes 30, the piezoelectric ceramic layer 10 expands and contracts, and the entire piezoelectric element 100 expands and contracts.

[0022] The piezoelectric ceramic layer 10 mainly contains an alkali niobate perovskite oxide having piezoelectric properties. The alkali niobate perovskite oxide has a perovskite structure. Metal oxides having a perovskite structure are generally represented by the composition formula ABO3 and consist of a metal element located at site A, a metal element located at site B, and oxygen. In an ideal perovskite structure, 12 oxygen atoms coordinate around the metal element at site A and 6 oxygen atoms coordinate around the metal element at site B, and this structure is periodically repeated to form a crystal. The crystalline phase of the alkali niobate perovskite oxide contained in the piezoelectric ceramic layer 10 is also called the "main phase". In this embodiment, the alkali-based perovskite oxide of niobate preferably contains at least one alkali metal (potassium (K), sodium (Na), lithium (Li), etc.) as an alkali component at site A, and is particularly preferably at least one of potassium (K) and sodium (Na). It is also preferable that niobium (Nb) is contained at site B. Furthermore, the A site may contain at least one alkaline earth metal (calcium (Ca), strontium (Sr), barium (Ba), etc.) as an alkali component. Moreover, the effects of the present invention can be obtained even if some of the alkali components are located at site B, or if niobium is located at site A.

[0023] Furthermore, although the compositional formula of a metal oxide having a perovskite-type structure is represented by the compositional formula ABO3 as described above, in reality, due to volatilization during firing and errors in compositional analysis, the ratio of the amount of metal elements at site A, site B, and oxygen in the entire alkali niobate-based perovskite-type oxide may not necessarily be 1:1:3. Even in such cases, if the piezoelectric ceramic layer 10 has a perovskite-type structure as its main structure, it is included within the scope of this disclosure. That the piezoelectric ceramic layer 10 has a perovskite-type structure as its main structure, that is, that the piezoelectric ceramic layer 10 contains a main phase containing a perovskite-type oxide, can be determined, for example, from the measurement results of XRD (X-ray Diffraction) or TEM (Transmission Electron Microscope) on the piezoelectric ceramic layer 10. That the piezoelectric ceramic layer 10 has a perovskite-type structure as its main structure means that, in the XRD or TEM measurement results, the characteristics of the perovskite-type structure are more pronounced than the characteristics of other crystal structures.

[0024] In this disclosure, the alkali niobate perovskite oxide contains at least one of Ni, Cu, and Ag. In the following description, the at least one element among Ni, Cu, and Ag contained in the alkali niobate perovskite oxide is also referred to as the "first metal element." The first metal element may be one element, two elements, or three elements, but it is preferable that it contains Ni. In this disclosure, the concentration [mol%] of the first metal element contained in the alkali niobate perovskite oxide in the active layer 14 is higher than the concentration [mol%] of the first metal element contained in the alkali niobate perovskite oxide in the inert layer 12. The method for determining the concentration and proportion of the metal element contained in the alkali niobate perovskite oxide will be described later.

[0025] The piezoelectric element 100 of this disclosure has improved piezoelectric properties and improved dielectric breakdown strength because the alkali niobate perovskite oxide contains a first metal element, and its concentration is higher in the active layer 14 than in the inert layer 12. Although the presumed mechanism is not certain, the following mechanism is presumed. First, it is presumed that the first metal element is positioned in place of Nb in the crystal structure of the alkali niobate perovskite oxide. It is thought that by solid-solubilizing the first metal element in the alkali niobate compound, distortion occurs in the crystal structure, and as a result, the piezoelectric properties (S / E) are improved. Here, the strength of the inert layer is considered important for dielectric breakdown resistance. As the solid-solubilization of the first metal element in the alkali niobate compound progresses, the strength of the inert layer 12 may decrease, but by making the concentration of the first metal element lower in the inert layer 12 than in the active layer 14, the decrease in the strength of the inert layer 12 can be suppressed. As a result, it is thought that the dielectric breakdown strength can be improved, thus making it possible to achieve both piezoelectric properties and dielectric breakdown strength simultaneously.

[0026] In the active layer 14, the concentration of the first metal element contained in the alkali niobate perovskite oxide is not particularly limited as long as it is higher than that of the inert layer 12, but is preferably 0.01 mol% or more and 3.0 mol% or less, more preferably 0.05 mol% or more and 1.5 mol%, even more preferably 0.1 mol% or more and 1.0 mol%, and even more preferably 0.2 mol% or more and 0.8 mol% or less. In the inert layer 12, the concentration of the first metal element contained in the alkali niobate perovskite oxide is not particularly limited as long as it is lower than that of the active layer 14, but is preferably less than 0.2 mol%, more preferably less than 0.1 mol%, even more preferably less than 0.01 mol%, and even more preferably below the detection limit.

[0027] Furthermore, in the active layer 14, the ratio of the first metal element to Nb contained in the alkali niobate perovskite oxide (first metal element [mol%] / Nb [mol%]) is not particularly limited, but is preferably 0.05% or more and 3.0% or less, more preferably 0.1% or more and 3.0%, even more preferably 0.5% or more and 2.5%, and even more preferably 0.5% or more and 2.0%. Furthermore, in the inert layer 12, the ratio of the first metal element to Nb contained in the alkali niobate perovskite oxide (first metal element [mol%] / Nb [mol%]) is not particularly limited, but is preferably 0.2% or less, more preferably 0.1% or less, and even more preferably 0.05% or less.

[0028] The concentration and proportion of metal elements contained in the crystal grains of the main phase containing alkali niobate perovskite-type oxide can be determined by performing qualitative and quantitative analysis using EPMA (Electron Probe Micro Analyzer) on the polished surface of the piezoelectric ceramic layer 10 in a cross-section parallel to the stacking direction D1 after firing. Specifically, first, the crystal grains of the main phase oxide are identified using a backscattered electron composition image at a magnification of 5000x using a scanning electron microscope (SEM) and a WDS (Wavelength-Dispersive X-ray Spectroscopy) image of EPMA in the same field of view, and at least three crystal grains of the main phase oxide included in the obtained image are randomly selected. The crystal grains that are estimated to contain alkali niobate perovskite-type oxide based on the EPMA measurement results are considered to be the crystal grains of the main phase. Next, qualitative and quantitative analysis using EPMA is performed on the selected crystal grains, and the amount (number of moles) of each metal element is calculated for each crystal grain. Then, the average (arithmetic mean) is calculated and this is the amount of the metal element contained in the alkali niobate perovskite oxide of the sample. Using the amounts of all the metal elements calculated, the concentration (mol%) of the above metal elements and the proportion of each metal element can be calculated.

[0029] The concentration (mol%) of the first metal element in an alkali niobate perovskite oxide is expressed as the proportion of the first metal element contained in a crystal particle whose main crystal structure is an alkali niobate perovskite oxide, with the total amount of all metal elements contained in that crystal particle being 100 mol%. In embodiments where the first metal element contains two types of metal elements (Ni and Cu, Ni and Ag, or Cu and Ag) or three types of metal elements (Ni, Cu, and Ag), the concentration (mol%) of the first metal element is expressed as the total concentration (mol%) of the multiple metal elements.

[0030] The cross-section of the piezoelectric ceramic layer 10 parallel to the stacking direction D1 is positioned as far away as possible from the side surface of the piezoelectric element 100. Furthermore, the position of the piezoelectric ceramic layer 10 to be analyzed by EPMA is near the center in the stacking direction D1 and in the direction parallel to the stacking direction D1, and approximately equidistant from the upper and lower internal electrodes 20 (electrodes 22 and 24). This is because piezoelectric ceramic layers 10 located close to the side surface of the piezoelectric element 100 may not be involved in the expansion and contraction of the piezoelectric element 100. Note that the results of the EPMA analysis will be approximately the same for the piezoelectric ceramic layer 10 sandwiched between electrodes 22 and 24.

[0031] Furthermore, from the viewpoint of improving piezoelectric properties and insulating properties, alkali niobate perovskite oxides preferably contain at least one of manganese (Mn) and titanium (Ti), and more preferably contain both Mn and Ti. It is believed that the addition of a predetermined amount of Mn improves insulating properties by causing Mn to solid dissolve in the Nb site as an acceptor and form oxygen vacancies. It is also believed that the addition of a predetermined amount of Ti changes the crystal structure and improves piezoelectric properties.

[0032] The main component of the alkali niobate perovskite-type oxide contained in the main phase (components excluding Ni, Cu, and Ag as the first metal element) is preferably a compound represented by the following compositional formula (1).

[0033] (K 1-a-b Naa M b ) c (Nb 1-d-e-f Mn d Zr e Ti f )O 3+g ···(1)

[0034] In the above compositional formula (1), the element M is at least one of alkaline earth metals Ba (barium), Ca (calcium), and Sr (strontium). In the compositional formula (1), theoretically, K (potassium), Na (sodium), and the element M are arranged at the A site of the perovskite structure, and Nb (niobium), Mn (manganese), Zr (zirconium), and Ti (titanium) are arranged at the B site.

[0035] As the values of the coefficients a to g in the above compositional formula (1), among the combinations of values that form the perovskite structure, preferable values are selected from the viewpoints of electrical properties (especially insulation) or piezoelectric properties (especially piezoelectric constant d33). Specifically, the coefficients a to f preferably satisfy 0 ≦ a ≦ 1.0, 0 ≦ b ≦ 1.0, 0 < a + b ≦ 1.0, 0.8 ≦ c ≦ 1.2, 0 ≦ d ≦ 0.3, 0 ≦ e ≦ 0.3, 0 ≦ f ≦ 0.3, and 0 ≦ d + e + f < 0.5. According to such an aspect, it is considered that the piezoelectric properties and insulation can be further improved. Furthermore, the coefficients a to f more preferably satisfy 0 < a < 0.9, 0 < b < 0.3, 0 < a + b < 1.0, 0.85 ≦ c ≦ 1.15, 0 < d ≦ 0.2, 0 < e ≦ 0.2, 0 < f ≦ 0.2, and 0 < d + e + f < 0.5. According to such an aspect, it is considered that the piezoelectric properties and insulation can be further improved.

[0036] Of the oxygen coefficient (3+g), the coefficient g is a positive or negative value indicating oxygen deficiency or excess, relative to the oxygen coefficient which is usually 3. The oxygen coefficient (3+g) can take any value that constitutes a perovskite-type oxide. A typical value for the coefficient g is g=0, and it is preferable that -0.1≦g≦0.1 is satisfied. The value of the coefficient g can be calculated from the electrical neutrality conditions of the main phase composition. However, compositions that deviate somewhat from the electrical neutrality conditions are also acceptable for alkali niobate-based perovskite-type oxides.

[0037] Furthermore, the alkali niobate perovskite oxide according to this embodiment may contain other elements as needed. For purposes such as improving piezoelectric and insulating properties, controlling sintering temperature, and suppressing grain growth, a composition containing at least one of the following elements may be added: Li, Ta, Sc, V, Cr, Fe, Co, Zn, Y, Mo, Ru, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, W, Re, Os, and Ir.

[0038] The piezoelectric ceramic layer 10 preferably further contains an oxide containing at least one of Mn and Ti, in addition to the main component, alkali niobate perovskite-type oxide, and more preferably contains an oxide containing both Mn and Ti. In the following description, the crystalline phase of the oxide containing at least one of Mn and Ti contained in the piezoelectric ceramic layer 10 will also be referred to as the "sub-phase." For this reason, the piezoelectric ceramic layer 10 preferably contains a sub-phase containing an oxide containing at least one of Mn and Ti, in addition to the main phase, and more preferably contains a sub-phase containing an oxide containing both Mn and Ti. The sub-phase is dispersed in a scattered manner within the main phase. In general, alkali niobate perovskite-type oxides have a cube-like particle shape, making them prone to voids and difficult to densify. However, by compounding a crystalline phase of an oxide containing at least one of Mn and Ti, a dense and reliable piezoelectric ceramic layer 10 can be obtained.

[0039] From the viewpoint of affinity with the main phase, the secondary phase preferably contains a Mn-Ti-O-based oxide (e.g., MnTi2O4, Mn2TiO4, MnTiO3-based oxide). By including a Mn-Ti-O-based oxide in the secondary phase, the deterioration of piezoelectric properties can be suppressed, and reliability can be further improved.

[0040] Mn-Ti-O oxides are oxides containing Mn (manganese) and Ti (titanium), and are represented, for example, by the following compositional formula (2).

[0041] MnTiO y ...(2)

[0042] In the above compositional formula (2), the coefficient y satisfies 2 ≤ y ≤ 8. The Mn-Ti-O oxide is preferably a spinel-type structure or an inverse spinel-type structure; for example, MnTi2O4 and Mn2TiO4 are preferred as the Mn-Ti-O oxide. This allows for the acquisition of a more reliable piezoelectric ceramic layer 10. Furthermore, the above standard numerical range may be deviated from as long as the structure can be maintained and the changes in the compound's properties are within an acceptable range. For example, the Mn-Ti-O oxide may be represented by the following compositional formula (3) or compositional formula (4).

[0043] Mn h Ti 2i O 4±j ...(3) Mn 2h Ti i O 4±j ...(4)

[0044] In the above compositional formulas (3) and (4), the coefficients h and i are respectively 0.8 < h < 1.2 and 0.8 < i < 1.2, and the coefficient j is a positive or negative value indicating oxygen deficiency or excess. Further, the Mn-Ti-O-based oxide may contain other elements as necessary. For example, it is possible to contain elements such as Na, K, Zr, Ba, Ca, Sr, Ni, Cu, Ag, Sc, etc. The secondary phase may contain a plurality of types of Mn-Ti-O-based oxides. Also, the secondary phase may contain oxides other than the Mn-Ti-O-based oxides. For example, manganese oxides (MnO x oxides, such as MnO, MnO2, Mn3O4, etc.), manganese and niobium oxides (Mn-Nb-O-based oxides, such as Mn4Nb2O9, MnNb2O6, etc.) may be included.

[0045] The crystal structures of the crystal particles of the main phase and the secondary phase can be identified using XRD or TEM. The cut surface and the position of the piezoelectric ceramic layer 10 used for identifying the crystal structure of the crystal particles of the main phase or the secondary phase can be determined under the same conditions as the cut surface and the position of the piezoelectric ceramic layer 10 used for measuring the concentration of the metal element of the main phase. Also, when it can be presumed that the composition and its distribution of the crystal particles of the main phase and the secondary phase are generally the same even outside the above positions (for example, when the thicknesses of each piezoelectric ceramic layer 10 are almost the same), XRD or TEM may be used to identify the regions other than the cut surface and the position used for measuring the metal element concentration of the main phase, or powder XRD may be performed on the powder including the piezoelectric ceramic layer 10 of the sample for identification.

[0046] In the present embodiment, the ratio of the secondary phase contained in the piezoelectric ceramic layer 10 is not particularly limited as long as the object of the present invention is not impaired, and for example, it can be 0.1% by volume or more and 30% by volume or less. Note that as the mixing ratio of the main phase and the secondary phase, it is most preferable to measure the porosity generated when firing the main phase alone in the firing profile to be implemented and add the secondary phase with a volume ratio that can fill the voids. In the case of the composition of the main phase in the examples described later, for example, 0.5% by volume or more and 2.0% by volume or less are preferable.

[0047] An example of a method for manufacturing the piezoelectric element 100 of this embodiment is described below. First, necessary raw material powders are selected from the main component raw material powders of the alkali niobate perovskite type oxide that will be the main phase, and weighed to obtain the desired composition. The main component raw material powders of the main phase may be oxides, carbonates, or hydroxides of each element contained in the main phase. Ethanol is added to these main phase raw material powders, and the mixture is wet-mixed in a ball mill for preferably 15 hours or more to obtain a slurry. The obtained slurry is dried, and the resulting mixed powder is calcined, for example, at 600 to 1100°C in an atmospheric environment for 1 to 10 hours to obtain calcined powder of the main component of the main phase.

[0048] Next, additives are selected as needed and weighed in a predetermined amount relative to the calcined powder of the main component of the main phase. The raw material powders of the additives may be oxides, carbonates, or hydroxides of each element added as additives to the alkali niobate perovskite-type oxide that forms the main phase. Then, ethanol is added to the powder mixed with the calcined powder of the main component of the main phase and the additives, and the mixture is wet-mixed in a ball mill for preferably 15 hours or more to obtain a slurry. The slurry is dried to obtain a mixed powder, which is then calcined, for example, at 600 to 1100°C in an atmospheric environment for 1 to 10 hours to produce the calcined powder of the main phase.

[0049] In this way, calcined powder of the main phase can be prepared. By preparing calcined powder of the main components of the main phase and then adding a first metal element as an additive, the piezoelectric properties of the main phase can be further improved. This is thought to be because segregation of the first metal element becomes less likely. Here, the main components of the main phase are the components excluding Ni, Cu, and Ag, and for example, in composition formula (1), this means K, Na, alkaline earth metal elements M, Nb, Mn, Zr, and Ti. Alternatively, instead of preparing calcined powder of the main components of the main phase, the calcined powder of the main components of the main phase may be prepared by mixing the raw material powder of the main components of the main phase and the raw material powder of the first metal element as an additive at the same time.

[0050] If the piezoelectric ceramic layer 10 contains a secondary phase, separately from the above, first, necessary materials are selected from the raw material powders of the oxides that will form the secondary phase and weighed to achieve the desired composition. The raw material powders of the secondary phase may be oxides, carbonates, or hydroxides of each element contained in the secondary phase. For example, they may be selected and weighed as needed from MnCO3, TiO2, etc. Compounds of other metal elements may also be added. Then, ethanol is added to these raw material powders of the secondary phase and wet-mixed in a ball mill for preferably 15 hours or more to obtain a slurry. The mixed powder obtained by drying the slurry is calcined, for example, at 600 to 1300°C in an atmospheric environment for 1 to 10 hours to produce calcined powder of the secondary phase.

[0051] As described above, the calcined powder of the main component and, if necessary, the calcined powder of the secondary phase are weighed in a predetermined ratio, a dispersant, a binder, and an organic solvent (e.g., toluene) are added, and the mixture is pulverized and mixed to obtain a slurry. For the mixing ratio of the main phase and secondary phase, it is most preferable to measure the void ratio generated when the main phase alone is calcined using the calcination profile to be implemented, and add a secondary phase in a volume ratio that can fill the voids. Subsequently, a ceramic green sheet is produced by processing the slurry into a sheet shape using a doctor blade method or the like. The film thickness per layer of the laminate can be controlled by adjusting the thickness of the green sheet. Furthermore, by adjusting the amount of the first metal element added during the slurry preparation stage, the content of the first metal element in the active layer 14 and the inert layer 12 can be controlled by separately producing green sheets for the active layer 14 and the inert layer 12.

[0052] Next, using a conductive paste for the internal electrode 20, an electrode layer, which will become the internal electrode 20, is formed on one surface of the ceramic green sheet, for example by screen printing. The electrode layer is mainly composed of nickel (Ni).

[0053] Subsequently, multiple ceramic green sheets, each with an electrode layer formed on it, are stacked so that the electrode layers are alternately exposed from both sides. Further stacking of ceramic green sheets without electrode layers is performed on both the front and back surfaces of the resulting laminate 90. The resulting laminate 90 is then heat-pressed to obtain a laminate 90 in which ceramic green sheets and electrode layers are alternately stacked. This laminate 90 is cut into a desired shape, and then a binder removal process is performed, for example, by holding it in an N2 atmosphere at a temperature of 200-400°C for 2-10 hours.

[0054] The laminate 90 after binder removal treatment is placed in an alumina setter, for example at 1050°C and an oxygen partial pressure of 10 -12 The material is fired in an atm reducing atmosphere for 5 hours. Then, it is annealed in an N2 atmosphere at 800°C for 10 hours. By firing it in an alumina setter, it can be manufactured stably, and by performing the N2 annealing treatment, a highly insulating laminate 90 can be obtained.

[0055] After the annealing treatment, the sides of the laminate 90 are polished as appropriate, and then a pair of external electrodes 30 made of, for example, Au are formed on the sides of the laminate 90 by, for example, a sputtering method. The pair of external electrodes 30 are formed so that they face each other with the laminate 90 in between. A polarization treatment is then performed on the laminate 90 on which the external electrodes 30 are formed. In this way, a piezoelectric element 100 can be obtained in which piezoelectric ceramic layers 10 and internal electrodes 20 are alternately laminated.

[0056] The manufacturing method described above is merely an example, and various other processes and processing conditions can be used to manufacture the piezoelectric element 100. For example, instead of adding the first metal element to the main phase, the firing conditions may be adjusted so that the first metal element diffuses from the electrode material during firing. Alternatively, instead of separately producing calcined materials of the main phase and the sub-phase beforehand and then mixing and firing the powders of both, the raw materials may be mixed in a quantity ratio corresponding to the final piezoelectric ceramic layer 10 composition and then fired. However, the method of separately producing calcined materials of the main phase and the sub-phase beforehand and then mixing them allows for more precise control of the composition of the main phase and the sub-phase, thereby increasing the yield of the piezoelectric ceramic layer 10.

[0057] In other embodiments of this disclosure, a component including a piezoelectric element 100 is provided. This component exhibits excellent piezoelectric properties and excellent dielectric breakdown strength. The component is not particularly limited, but examples include components for various applications such as vibration detection, pressure detection, oscillation, and piezoelectric devices. Furthermore, in other embodiments of this disclosure, a device including such a component is provided. This device exhibits excellent piezoelectric properties and excellent dielectric breakdown strength. The device is not particularly limited, but examples include actuators, haptics, buzzers, ultrasonic sensors, and the like.

[0058] Figure 2 is a schematic diagram showing an example of the general configuration of an actuator 200 as a device 150. The actuator 200 is not particularly limited, but for example, it may be used in the opening and closing control unit of a valve in a mass flow controller or in the stage drive unit of a precision positioning device to displace a driven object. The actuator 200 shown in Figure 2 consists of an actuator body 205, terminals (drive terminals 226, 227 and output terminals 246, 247, 248), a mesh 230, a strain gauge 240, a seat 250, and a cap 260, and expands and contracts when a voltage is applied. The actuator 200 has a strain gauge 240 connected to an actuator body 205 having a plurality of piezoelectric elements 100 via a mesh 230. The plurality of piezoelectric elements 100 are arranged in series in the stacking direction D1, and their end faces are bonded together with adhesive. The actuator body 205 may be formed from a single piezoelectric element 100 instead of a plurality of piezoelectric elements 100. The strain gauge 240 is provided with output terminals 246, 247, and 248. This allows the actuator 200 equipped with the strain gauge 240 to receive signals of deformation of the piezoelectric element 100 via the output terminals 246, 247, and 248 of the strain gauge 240.

[0059] Figure 3 is a cross-sectional view showing an example of a schematic configuration of the haptics 300 as device 150. The haptics 300 is not particularly limited, but may include, for example, a piezoelectric element 100 and a vibrating body in contact with it. The haptics 300 shown in Figure 3 is a device that includes a touch-sensitive display 310 and provides tactile feedback in response to an operating signal. The touch-sensitive display 310 forms the upper surface of the housing 320 and is in contact with the display 330. Inside the housing 320 is housed the piezoelectric element 100, which is bonded to a substrate 340. The substrate 340 bends as the piezoelectric element 100 contracts, either as a result of charge accumulation in the piezoelectric element 100 or in response to an external force applied to the touch-sensitive display 310, as indicated by the white arrow.

[0060] Figure 4 is a cross-sectional view showing an example of the schematic configuration of a buzzer 400 as a device 150. The buzzer 400 is not particularly limited, but may include, for example, a piezoelectric element 100 and a diaphragm in contact with it. The buzzer 400 shown in Figure 4 has a substantially disc-shaped external form and comprises a plastic case 410, a piezoelectric diaphragm 420 built into the case 410, and a piezoelectric element 100 in contact with the piezoelectric diaphragm 420. The case 410 is integrally formed of a cylindrical support ring 412 and a circular top plate 414 positioned to close the opening at one end of the support ring 412. A circular sound-emitting hole 430 that penetrates in the thickness direction is formed in the center of the top plate 414. The piezoelectric diaphragm 420 is a circular plate material in plan view and is fitted and joined to close the opening at the other end of the support ring 412. Inside the case 410, a resonance space 440 is formed between the top plate 414 and the piezoelectric diaphragm 420. The resonance space 440 resonates in accordance with the vibration of the piezoelectric diaphragm 420. When a voltage is applied to the piezoelectric element 100, the piezoelectric diaphragm 420 vibrates, and sound waves generated from the piezoelectric diaphragm 420 are radiated to the outside through the sound emission holes 430.

[0061] Figure 5 is a cross-sectional view showing an example of the schematic configuration of an ultrasonic sensor 500 as a device 150. The ultrasonic sensor 500 is not particularly limited, but for example, it may include a piezoelectric element 100 and a diaphragm in contact with it, wherein when a voltage is applied to the piezoelectric element 100, the diaphragm vibrates and emits ultrasonic waves, and when the diaphragm receives the ultrasonic waves, the piezoelectric element 100 outputs a voltage. The ultrasonic sensor 500 shown in Figure 5 has a bottomed cylindrical case 510 having an opening 512 at one end in the axial direction, a piezoelectric element 100 fixed to the inside of the bottom surface of the bottomed cylindrical case 510, an acoustic matching layer 520 fixed to the outside of the bottom surface of the bottomed cylindrical case 510 so as to face the piezoelectric element 100, a base member 530 that closes the opening 512 of the bottomed cylindrical case 510, and a pair of input / output terminals 540, 550 fixed to the base member 530 and electrically connected to the piezoelectric element 100. [Examples]

[0062] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0063] 1. Sample preparation A calcined powder of the main phase containing an alkali niobate perovskite-type oxide and a calcined powder of the secondary phase containing an oxide containing Mn and Ti were produced. The composition of the main metal elements of the main phase was (K 0.46 Na 0.47 Ba 0.07 )(Nb 0.87 Mn 0.03 Ti 0.03 Zr 0.07 To achieve the desired result, K2CO3 powder, Na2CO3 powder, BaCO3 powder, Nb2O5 powder, MnCO3 powder, TiO2 powder, and ZrO2 powder were weighed out as the main component raw material powders for the main phase. Ethanol was added to these main component raw material powders for the main phase, and the mixture was wet-mixed in a ball mill for more than 15 hours to obtain a slurry. Next, the slurry was dried to obtain a mixed powder, which was then calcined at 930°C in an air atmosphere for 4 hours to produce calcined powder of the main component of the main phase.

[0064] Next, Ni was used as the first metal element, and NiO powder was weighed and added as the raw material powder for the additive to the main phase so that the Ni content reached a predetermined concentration (mol%) relative to the total metal elements of the main phase containing the Ni to be added. Then, the raw material powder for the additive was added to the calcined powder of the main component of the main phase, ethanol was added to the mixed raw material powder, and the mixture was wet-mixed in a ball mill for more than 15 hours to obtain a slurry. The slurry was dried, and the resulting mixed powder with the added additive was calcined at 930°C in an air atmosphere for 4 hours to produce the calcined powder of the main phase containing the first metal element.

[0065] Separately, MnCO3 powder and TiO2 powder were weighed out as raw material powders for the secondary phase, so that the crystalline structure of the secondary phase would be an oxide of Mn2TiO4. Ethanol was added to these secondary phase raw material powders and wet-mixed in a ball mill for more than 15 hours to obtain a slurry. The slurry was dried to obtain a mixed powder, which was then calcined at 1150°C in an air atmosphere for 5 hours to produce calcined secondary phase powder.

[0066] Next, the calcined powders of the main phase and the secondary phase were weighed so that the ratio of the calcined powder of the secondary phase to the calcined powder of the main phase was 1.5% by volume. Then, a dispersant, a binder, and an organic solvent were added to the weighed calcined powders of the main phase and secondary phase, and the mixture was pulverized and mixed to obtain a slurry. Next, a ceramic green sheet was produced by processing the slurry into a sheet shape using the doctor blade method. At this time, the thickness of the ceramic green sheet was controlled by the height of the blade of the doctor blade device.

[0067] Next, using a conductive paste for internal electrodes, an electrode layer mainly composed of Ni was screen printed onto one surface of a ceramic green sheet, so that the electrode thickness after firing would be approximately 2 μm. Multiple ceramic green sheets printed with conductive paste were stacked and heat-pressed together so that the conductive paste was exposed alternately from both sides. The inert layer 12 was laminated so that it was located on both the top and bottom of the laminate. For the formation of the active layer 14 and the inert layer 12, ceramic green sheets with pre-adjusted amounts of Ni were used. The thickness of the inert layer 12 after firing was approximately 100 μm. The thickness of each layer of the active layer 14 after firing was approximately 50 μm. The thickness of each layer of the internal electrode 20 after firing was approximately 2 μm. There were 10 layers of active layer 14. After that, the sheets were cut to a depth of 8 mm × width of 8 mm. Then, a binder removal treatment was performed by holding the sheets in a nitrogen atmosphere at a temperature of 300°C for 5 hours.

[0068] The laminate 90 after binder removal treatment is placed in an alumina setter at 1050°C and an oxygen partial pressure of 10 -12The laminate was fired in an atm reducing atmosphere for 5 hours. After that, it was annealed in an N2 atmosphere at 800°C for 10 hours. After the annealing treatment, the top, bottom, and sides of the laminate 90 were polished as appropriate, and then a pair of external electrodes 30 made of Au were formed on the sides of the laminate 90 by sputtering. Then, the laminate 90 with the external electrodes 30 formed was placed in 40°C silicon oil and subjected to polarization treatment by applying a DC electric field of 3kV / mm for 15 minutes to obtain piezoelectric elements 100 of samples 1 to 8.

[0069] 2.Measurement method The main phase metal elements were analyzed for the piezoelectric elements 100 of samples 1 to 8. In addition, dielectric breakdown tests were performed on the piezoelectric elements 100 of samples 1 to 8, and the S / E value was determined by measuring the displacement when an electric field was applied.

[0070] (1) Analysis of the main phase metal elements For each sample, a piezoelectric ceramic layer 10 was selected near the center of a cross-section passing through the center of the top surface and parallel to the stacking direction D1, and approximately equidistant from the upper and lower electrodes 22 and 24. Quantitative analysis was then performed using EPMA. First, the crystal grains of the main phase, alkali niobate perovskite oxide, were identified using a COMPO image at 5000x magnification with an SEM. Next, a WDS image was taken in the same field of view, and three crystal grains of the main phase oxide were randomly selected from the obtained image. Then, quantitative analysis was performed on the selected crystal grains using EPMA, and the amount (number of moles) of each metal element was calculated for each crystal grain. The average (arithmetic mean) was then calculated and used as the amount of that metal element contained in the alkali niobate perovskite oxide of that sample. The concentration (mol%) of all metal elements was calculated using the amounts of all the metal elements obtained.

[0071] (2) Dielectric breakdown test For each piezoelectric element 100 of the sample, a DC voltage of 1.0 kV / mm at room temperature and in 1-minute intervals was applied to determine the electric field at which the element was destroyed. For reliability evaluation, elements were classified as A if the electric field value (kV / mm) at which the element was destroyed in the dielectric breakdown test was 10 or greater, and B if it was less than 10.

[0072] (4) Measurement of S / E A positive electric field was applied to the sample at room temperature using a sinusoidal wave of several hundred Hz, and the displacement S along the stacking direction D1 was measured. This displacement S was divided by the electric field E to calculate the S / E value (pm / V) for each electric field. For evaluation of S / E, a value of 200 or more was designated as A, and a value less than 200 was designated as B.

[0073] 3.Results The results are shown in Table 1 below. In Table 1, "-" indicates that the elemental analysis was below the detection limit. Furthermore, as a representative example of the analysis results for the main phase metal elements, the ratios of elements other than Ni and Nb are shown in Table 2 below. Note that there was a variation of approximately ±3% for each element depending on the sample.

[0074] [Table 1]

[0075] [Table 2]

[0076] Sample 1, which did not contain Ni as the first metal element in either the active layer 14 or the inert layer 12, had a low S / E value and poor piezoelectric properties. Similarly, Sample 2, in which the concentration of the first metal element in the inert layer 12 was higher than that in the active layer 14, had a low electric field value at which dielectric breakdown occurred and poor dielectric breakdown strength. In contrast, Samples 3-8, in which the concentration of the first metal element in the active layer 14 was higher than that in the inert layer 12, exhibited excellent piezoelectric properties and superior dielectric breakdown strength.

[0077] The present invention is not limited to the embodiments described above, and can be realized in various configurations without departing from its spirit. For example, the technical features in the embodiments and examples corresponding to the technical features in each form described in the summary of the invention can be replaced or combined as appropriate in order to solve some or all of the above-described problems, or to achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate. [Explanation of symbols]

[0078] 10...Piezoelectric ceramic layer, 12...Inert layer, 14...Active layer, 20...Internal electrode, 22, 24...Electrode, 30...External electrode, 90...Laminate, 100...Piezoelectric element, 150...Device, 200...Actuator, 205...Actuator body, 226, 227...Drive terminals, 230...Mesh, 240...Strain gauge, 246, 247, 248...Output terminal, 250...Seat, 260...Cap, 300...Haptics, 31 0…Touch-sensitive display, 320…Housing, 330…Display, 340…Substrate, 400…Buzzer, 410…Case, 412…Support ring, 414…Top plate, 420…Piezoelectric diaphragm, 430…Sound emission hole, 440…Resonance space, 500…Ultrasonic sensor, 510…Bottomed cylindrical case, 512…Opening, 520…Acoustic matching layer, 530…Base member, 540, 550…Input / output terminals, D1…Lamination direction, S1…End face

Claims

1. A piezoelectric element comprising a piezoelectric ceramic layer mainly composed of an alkali niobate perovskite oxide and an internal electrode mainly composed of Ni, which are alternately stacked, The alkali niobate perovskite-type oxide contains a first metal element which is at least one of Ni, Cu, and Ag. The piezoelectric ceramic layer is An inert layer located at the end face in the stacking direction, The active layer located inside the stacking direction, It has, The concentration [mol%] of the first metal element contained in the alkali niobate perovskite oxide in the active layer is higher than the concentration [mol%] of the first metal element contained in the alkali niobate perovskite oxide in the inert layer. A piezoelectric element characterized by the following features.

2. In the piezoelectric element according to claim 1, The first metal element includes Ni, A piezoelectric element characterized by the following features.

3. In the piezoelectric element according to claim 1, In the active layer, the ratio of the first metal element to Nb contained in the alkali niobate perovskite oxide (first metal element [mol%] / Nb [mol%]) is 0.1% or more and 3.0% or less. In the inert layer, the ratio of the first metal element to Nb contained in the alkali niobate perovskite oxide (first metal element [mol%] / Nb [mol%]) is 0.05% or less. A piezoelectric element characterized by the following features.

4. In the piezoelectric element according to claim 1, The piezoelectric ceramic layer further contains an oxide comprising at least one of Mn and Ti. A piezoelectric element characterized by the following features.

5. In the piezoelectric element according to claim 1, The aforementioned alkali-based perovskite-type oxide of niobate contains at least one of Mn and Ti. A piezoelectric element characterized by the following features.

6. A component comprising a piezoelectric element according to any one of claims 1 to 5.

7. An apparatus comprising the component described in claim 6.

8. The apparatus according to claim 7, wherein the apparatus is one of an actuator, a haptic, a buzzer, and an ultrasonic sensor.

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