Piezoelectric elements and their applications

Abstract

This invention provides a technology that can improve the high-temperature durability of lead-free piezoelectric elements. [Solution] A piezoelectric element comprising a piezoelectric ceramic layer mainly composed of an alkali niobate perovskite oxide and an internal electrode mainly composed of a base metal, which are alternately stacked, wherein the number of pores formed in the piezoelectric ceramic layer is 100 μm. 2 It is characterized by having 50 or fewer items per unit.

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 sometimes used in high-temperature environments exceeding 100°C. Therefore, it is desirable that their insulation resistance degrades minimally even in high-temperature environments. However, the piezoelectric elements described in Patent Documents 1 and 2 had room for improvement in terms of suppressing the degradation of insulation resistance when used in high-temperature environments exceeding 100°C, i.e., in terms of high-temperature durability. Therefore, there was a need for a technology that could improve high-temperature durability in lead-free piezoelectric elements. [Means for solving the problem]

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

[0006] (1) According to one aspect of the present disclosure, a piezoelectric element is provided. This piezoelectric element is a piezoelectric element in which a piezoelectric ceramic layer containing an alkali niobate perovskite-type oxide as a main component and an internal electrode containing a base metal as a main component are alternately laminated, and the number of pores formed in the piezoelectric ceramic layer is 50 or less per 100 μm 2 This is characterized by the above. According to the piezoelectric element of this aspect, the high-temperature durability of the piezoelectric element can be improved.

[0007] (2) In the piezoelectric element described in (1) above, the number of pores formed in the piezoelectric ceramic layer may be 3 or more and 50 or less per 100 μm 2 This is characterized by the above. According to the piezoelectric element of this aspect, it is possible to suppress a decrease in the displacement characteristics of the piezoelectric element.

[0008] (3) In the piezoelectric element described in (1) or (2) above, the piezoelectric ceramic layer may further contain an oxide containing at least one of Mn and Ti. According to the piezoelectric element of this aspect, a dense and highly reliable piezoelectric ceramic layer can be obtained, and as a result, a decrease in piezoelectric characteristics can be suppressed.

[0009] (4) In the piezoelectric element described in any one of (1) to (3) above, the alkali niobate perovskite-type oxide may contain at least one of Mn and Ti. According to the piezoelectric element of this aspect, the piezoelectric characteristics and insulation properties are excellent.

[0010] (5) According to another aspect of the present disclosure, a component including the piezoelectric element described in any one of (1) to (4) above is provided. According to the component of this aspect, it has excellent high-temperature durability.

[0011] (6) According to another aspect of the present disclosure, an apparatus including the component described in (5) above is provided. According to the apparatus of this aspect, it has excellent high-temperature durability.

[0012] (7) In other forms of the present disclosure, the apparatus described in (6) above is provided to be an actuator, a haptic, a buzzer, and an ultrasonic sensor. This form of apparatus is superior in terms of high temperature resistance.

[0013] Furthermore, this disclosure can be implemented in various forms, for example, in the form of a method for manufacturing a piezoelectric element, a method for manufacturing a component containing such a piezoelectric element, a method for manufacturing an apparatus containing such a component, and so on. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic cross-sectional view showing the general configuration of a piezoelectric element. [Figure 2] This is a schematic diagram showing an example of the general configuration of an actuator as a device. [Figure 3] This is a cross-sectional view showing an example of the schematic configuration of a haptics device. [Figure 4] This is a cross-sectional view showing an example of the general configuration of a buzzer as a device. [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]

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] The internal electrode 20 of this embodiment contains a base metal as its main component. The base metal is not particularly limited and examples include Ni (nickel) and Cu (copper), but it is preferable that it contains Ni as its main component. By containing a base metal as its main component in 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) and Pt (platinum) are the main components. In addition to the base metal main component, the internal electrode 20 may also contain one or more other elements such as Cu, Ni, Ag (silver), Pd (palladium), and Pt (platinum). The external electrode 30 of this embodiment is formed with gold (Au) as its main component, but it is not limited to Au and may contain metals such as Pt, Ag, Pd, Ni, and 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, causing the entire piezoelectric element 100 to expand and contract.

[0021] The inventors of the present invention have found that the high-temperature durability of the piezoelectric element 100 can be improved by controlling the number of pores formed in the piezoelectric ceramic layer 10, as shown in the embodiments described below. The number of pores formed in the piezoelectric ceramic layer 10 of the present disclosure is 100 μm. 2 There are 50 or fewer per unit. The estimated mechanism by which this configuration improves the high-temperature durability of the piezoelectric element 100 is not clear, but the following mechanism is estimated. That is, the number of pores formed in the piezoelectric ceramic layer 10 is 100 μm. 2 By having 50 or fewer grains per unit area, the strength of the grain boundaries can be increased, which suppresses the deterioration of insulation even at high temperatures, and as a result, durability can be improved. As a result, the piezoelectric element 100 of this disclosure can be driven well even in high-temperature environments of 100°C or higher.

[0022] The number of pores formed in the piezoelectric ceramic layer 10 is set to 100 μm, from the viewpoint of suppressing a decrease in the displacement characteristics of the piezoelectric element 100. 2It is preferably three or more per 100 μm. The number of pores formed in the piezoelectric ceramic layer 10 is 100 μm 2 By being three or more per 100 μm, for example, residual stress generated during firing can be reduced, and as a result, it is considered that piezoelectric characteristics can be improved. The number of pores formed in the piezoelectric ceramic layer 10 is 100 μm from the viewpoint of achieving both high-temperature durability and piezoelectric characteristics 2 Per 100 μm, it is preferably three or more and 50 or less, more preferably five or more and 25 or less, still more preferably six or more and 15 or less, and even more preferably seven or more and 13 or less.

[0023] In the present disclosure, "pores formed in the piezoelectric ceramic layer 10" means those having a pore diameter of 50 nm or more. In the present disclosure, "pore diameter" means the average circle equivalent radius of the pores, which is calculated from the area of the pores. The number and pore diameter of the pores can be determined based on a scanning electron microscope (SEM) image. The number of pores formed in the piezoelectric ceramic layer 10 (per 100 μm 2 Per) is obtained by determining the number of pores formed per 100 μm in the SEM images of the 10 μm × 10 μm range at any three locations in the piezoelectric ceramic layer 10 and calculating the average value thereof. The imaging positions of any three locations are the regions sandwiched between the electrode 22 and the electrode 24 in the active layer 14. 2 As a more specific method for determining the number of pores, first, for the cross-section of a sample obtained by mirror-polishing the piezoelectric element 100 by ion milling, a backscattered electron image is acquired using SEM at an acceleration voltage of 5.0 kV and a magnification of 10,000 times. For the image cut out in the range of 10 μm × 10 μm, by performing binarization to make the ceramic part black and the pore part white by image analysis, both are clarified. For binarization, Gaussian blur (radius 2 pixels) is performed and the threshold value determined by the Huang method is used. After image analysis, in three images, the circle equivalent radius is calculated from the area of each pore part, and for pores having a circle equivalent radius of 50 nm or more, per 100 μm​​​​2 The number of stomata can be determined by counting how many are formed in each area and calculating the average value.

[0025] The number of pores formed in the piezoelectric ceramic layer 10 can be controlled, for example, by controlling at least one of the following: the particle size of the ceramic sheet, the heating rate during firing, the maximum temperature, and the holding time. Specifically, the smaller the particle size of the ceramic sheet, and the higher the maximum temperature during firing, the more the sintering progresses and the more densely packed the material becomes, resulting in a decrease in the number of pores. The longer the holding time, the smaller the pore diameter tends to be. Furthermore, the particle size of the ceramic sheet can be adjusted, for example, by controlling the mixing time in mixing using a ball mill, and the longer the mixing time, the smaller the particle size tends to be.

[0026] 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". The alkali niobate perovskite oxide 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). Furthermore, it is preferable that the B site contains niobium (Nb). In addition, the A site may contain alkaline earth metals (at least one of calcium (Ca), strontium (Sr), barium (Ba), etc.) as alkaline components. Moreover, the effects of the present invention can be obtained even if some of the alkaline components are located at the B site or niobium is located at the A site.

[0027] Alkali niobate perovskite oxides preferably contain at least one of manganese (Mn) and titanium (Ti), and more preferably both Mn and Ti, from the viewpoint of improving piezoelectric properties and insulating properties. 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. Furthermore, alkali niobate perovskite oxides are preferably represented by the following compositional formula (1).

[0028] (A1 a M1 b ) c (Nbd1 Mn d2 Ti d3 Zr d4 Sc d5 )O 3+e ···(1)

[0029] Element A1 is at least one of Li, Na, and K which are alkali metals. Element M1 is at least one of Ba, Ca, and Sr which are alkaline earth metals. In the above composition formula (1), element A1 and element M1 are arranged at the A site of the perovskite structure, and Nb, Mn, Ti, Zr, and Sc are arranged at the B site of the perovskite structure.

[0030] As the values of the coefficients a to e in the above composition formula (1), among the values for which the perovskite structure is established, preferable values are selected from the viewpoints of the electrical properties or piezoelectric properties of the lead-free piezoelectric composition.

[0031] Specifically, the coefficients a and b satisfy 0 < a < 1 and 0 < b < 1, and a = 0 (a composition not containing any alkali metal) and b = 0 (a composition not containing any of Ba, Ca, and Sr) are excluded. Also, it is preferable that a + b = 1. The coefficient c with respect to the entire A site satisfies 0.80 < c < 1.10, and preferably satisfies 0.90 ≤ c ≤ 1.05.

[0032] The coefficients d1, d2, d3, d4, and d5 satisfy 0 < d1 < 1, 0 < d2 < 1, 0 < d3 < 1, 0 ≤ d4 < 1, and 0 ≤ d5 < 1. However, d1 = 0 (composition不含Nb), d2 = 0 (composition不含Mn), and d3 = 0 (composition不含Ti) are excluded. The coefficient d4 of Zr and the coefficient d5 of Sc may be zero (i.e., the composition不含Zr or Sc may be acceptable). The coefficient d1 of Nb preferably satisfies 0.830 ≤ d1 ≤ 0.959. The coefficient d2 of Mn preferably satisfies 0.001 ≤ d2 ≤ 0.10. The coefficient d3 of Ti preferably satisfies 0.005 ≤ d3 ≤ 0.10. The coefficient d4 of Zr preferably satisfies 0 ≤ d4 ≤ 0.20. Also, it is preferable that d1 + d2 + d3 + d4 + d5 = 1. Among the coefficients 3 + e of oxygen, the coefficient e is a positive or negative value indicating oxygen deficiency or excess with respect to the coefficient of oxygen which is usually 3. The coefficient 3 + e of oxygen can take a value such that the main phase constitutes a perovskite oxide. A typical value of the coefficient e is e = 0, and 0 ≤ e ≤ 0.1 is preferable. Note that the value of the coefficient e can be calculated from the electrical neutrality condition of the composition of the main phase. However, as the composition of the main phase, a composition slightly deviating from the electrical neutrality condition is also acceptable.

[0033] According to the aspect in which the alkali niobate perovskite-type oxide is represented by the above compositional formula (1), it is excellent in piezoelectric properties and insulation properties. Although the estimation mechanism for this is not clear, the following mechanism is estimated. That is, it is considered that when a predetermined amount of Mn is added, Mn solid-solves into the Nb site as an acceptor and forms oxygen vacancies, thereby improving the insulation properties. Also, it is considered that when a predetermined amount of Ti is added, the crystal structure changes and the piezoelectric properties are improved.

[0034] For the alkali niobate perovskite-type oxide, in the above compositional formula (1), it is preferable to satisfy 0 < d5 < 1. That is, it is preferably excluded that d5 = 0 (composition不含Sc). Also, the coefficient d5 of Sc preferably satisfies 0.0002 ≤ d5 ≤ 0.10.

[0035] According to the aspect in which the alkali niobate perovskite-type oxide satisfies 0 < d5 < 1 in the above composition formula (1), that is, the aspect containing Sc, the insulation property can be further improved. Specifically, since the generation of carriers is suppressed by Sc acting as an acceptor, it is considered that the insulation property is further improved.

[0036] Furthermore, in the aspect in which the alkali niobate perovskite-type oxide satisfies 0 < d5 < 1 in the above composition formula (1), the content ratio of Sc to Ti (Sc / Ti) is preferably 0.004 or more and 8 or less in terms of molar ratio. When the content ratio of Sc to Ti is within this range, the piezoelectric properties are further excellent, and the insulation property under high-temperature conditions is further excellent.

[0037] The alkali niobate perovskite-type oxide is more preferably represented by the following composition formula (2). Note that the following composition formula (2) corresponds to a sub-concept of the above composition formula (1).

[0038] (K a1 Na a2 Li a3 Ba b1 Ca b2 Sr b3 ) c (Nb d1 Mn d2 Ti d3 Zr d4 Sc d5 )O 3+e ···(2)

[0039] The above compositional formula (1) and the above compositional formula (2) are equivalent, a1 + a2 + a3 = a, and b1 + b2 + b3 = b. The coefficient a1 of K satisfies 0 < a1 ≤ 0.7, and preferably satisfies 0.095 ≤ a1 ≤ 0.665. The coefficient a2 of Na satisfies 0 < a1 ≤ 0.9, and preferably satisfies 0.285 ≤ a2 ≤ 0.855. The coefficient a3 of Li satisfies 0 ≤ a3 ≤ 0.2, and preferably satisfies 0 ≤ a3 ≤ 0.1. The coefficient b1 of Ba satisfies 0 ≤ b1 ≤ 0.2, and preferably satisfies 0 ≤ b1 ≤ 0.1. The coefficient b2 of Ca satisfies 0 ≤ b2 ≤ 0.2, and preferably satisfies 0 ≤ b2 ≤ 0.1. The coefficient b3 of Sr satisfies 0 ≤ b3 ≤ 0.2, and preferably satisfies 0 ≤ b3 ≤ 0.1.

[0040] According to the aspect in which the alkali niobate perovskite-type oxide is represented by the above compositional formula (2), the piezoelectric properties are further improved. Specifically, by setting the coefficients a and b within the above ranges, the crystal structure is further optimized, and it is considered that the piezoelectric properties are further improved.

[0041] In addition, the alkali niobate perovskite oxide according to the present embodiment may contain other elements as necessary. For the purposes of improving piezoelectric properties and insulation properties, controlling sintering temperature, suppressing crystal grain growth, etc., for example, a composition containing at least one of Ta, Ni, Cu, 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, Ir, Ag, Si may be added.

[0042] 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 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 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 ceramic can be obtained.

[0043] The amount of the secondary phase relative to the main phase is preferably 0.1 to 20 volume%, and more preferably 0.5 to 5 volume%. 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 decrease in piezoelectric properties can be suppressed, and reliability can be further improved.

[0044] Mn-Ti-O oxides are oxides containing Mn (manganese) and Ti (titanium), and are represented, for example, by the following compositional formula (3).

[0045] MnTiO y ...(3)

[0046] The coefficient y satisfies 2 ≤ y ≤ 8. The Mn-Ti-O-based oxide preferably has a spinel structure or an inverse spinel structure. For example, as the Mn-Ti-O-based oxide, MnTi2O4 and Mn2TiO4 are preferred. By doing so, a more reliable piezoelectric ceramic can be obtained. Also, as long as the structure can be maintained and the change in the properties of the compound is within an acceptable range, it may deviate from the above standard numerical range. For example, the Mn-Ti-O-based oxide may have a structure represented by the following compositional formula (4) or compositional formula (5).

[0047] Mn f Ti 2g O 4±j ···(4) Mn 2h Ti i O 4±j ···(5)

[0048] In the above compositional formulas (4) and (5), the coefficients f, g, h, and i are respectively 0.80 < f < 1.2, 0.8 < g < 1.2, 0.8 < h < 1.2, and 0.8 < i < 1.2, and the coefficient j is a value indicating oxygen deficiency or excess. Also, other elements may be contained as necessary. For example, it is possible to contain elements such as Na, K, Zr, Ba, Ca, Sr, Ni, Cu, Ag, and Sc.

[0049] From the viewpoint of suppressing the decrease in insulation, the Mn-Ti-O-based oxide preferably contains Mn (manganese) and further contains Sc (scandium). That is, the piezoelectric ceramic layer 10 more preferably further contains an oxide containing Mn, Ti, and Sc in addition to the alkali niobate-based perovskite-type oxide. The Mn-Ti-O-based oxide is more preferably an oxide containing Sc in a proportion of 0.05 mol% or more and 5 mol% or less from the viewpoint of further improving the insulation.

[0050] Also, the piezoelectric ceramic layer 10 contains, in addition to the Mn-Ti-O-based oxide, MnO such as MnO, MnO2, or Mn3O4 xIt may also contain a mixture of oxides or Mn-Nb-O-based oxides (e.g., Mn4Nb2O9, MnNb2O6-based oxides), and MnO x Sc may be added to oxides such as Mn-Nb-O oxides.

[0051] An example of a method for manufacturing the piezoelectric element 100 of this embodiment is described below. First, several types of raw material powders necessary for forming the main phase are prepared, and these raw material powders are weighed to achieve the desired composition. The raw material powders may be oxides of each element contained in the main phase, carbonates of each element, hydroxides of each element, or compounds containing multiple elements contained in the main phase. Ethanol is added to the mixture of each weighed raw material powder, and the mixture is wet-mixed using a ball mill, preferably for 15 hours or more, to obtain a slurry. The obtained slurry is dried, and the resulting mixed powder is calcined, for example, under atmospheric conditions at a temperature of 600 to 1000°C for 1 to 10 hours to obtain a powdered main phase calcined powder.

[0052] To the obtained main phase calcined powder, a dispersant, a binder, and an organic solvent (e.g., toluene) are added, and the mixture is crushed and mixed using a ball mill or the like to obtain a slurry. At this time, by controlling the mixing time using the ball mill or the like, the ceramic sheet can be made to have various particle sizes. Subsequently, a ceramic green sheet is produced by processing the slurry into a sheet shape using a doctor blade method or the like. Then, using a conductive paste for internal electrodes, an electrode layer that will become the internal electrode 20 is formed on one surface of the ceramic green sheet, for example by screen printing.

[0053] Multiple ceramic green sheets, each having an electrode layer formed on it, are stacked so that the electrode layers are alternately exposed from both sides. On both the front and back surfaces of the resulting laminate 90, ceramic green sheets without electrode layers are further stacked. By pressing the resulting laminate 90 together, a laminate 90 is obtained 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 to 400°C for 2 to 10 hours.

[0054] The laminate 90, after binder removal, is fired for 2 to 5 hours under conditions of, for example, a temperature of 1000 to 1200°C and a reducing atmosphere where the pressure is controlled to be at least one order of magnitude lower than the equilibrium oxygen partial pressure of Ni / NO. Subsequently, it is annealed for 10 hours at, for example, 800°C in an N2 atmosphere. By performing the annealing treatment, a laminate 90 with a stable piezoelectric ceramic structure can be obtained.

[0055] After the sides of the laminated body 90 have been fired are polished as appropriate, and then a pair of external electrodes 30 are formed on the sides of the laminated body 90, for example, by sputtering using gold (Au). In addition to sputtering, a conductive paste containing silver (Ag), copper (Cu), etc. may be applied and baked at approximately 600°C to 900°C. The pair of external electrodes 30 are formed facing each other with the laminated body 90 in between. A polarization treatment is then performed on the laminated body 90 on which the external electrodes 30 have been 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 above manufacturing method is merely an example, and various other processes and processing conditions can be used to manufacture the piezoelectric element 100. For example, if the piezoelectric ceramic layer 10 contains a subphase, several types of raw material powders necessary for forming the subphase may be prepared, and these raw material powders may be used to produce a powdered subphase calcined powder as appropriate. More specifically, for example, ethanol may be added to the raw material powder and wet-mixed using a ball mill, preferably for 15 hours or more, to obtain a slurry, which is then dried. The resulting powder may then be calcined, for example, under an atmospheric environment at a temperature of 600 to 1300°C for 1 to 10 hours to produce a powdered subphase calcined powder. The obtained subphase calcined powder may then be mixed with the main phase calcined powder in a predetermined ratio as appropriate.

[0057] In other embodiments of this disclosure, a component including a piezoelectric element 100 is provided. This component offers excellent high-temperature durability, thus suppressing a decrease in reliability. 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 offers excellent high-temperature durability, thus suppressing a decrease in reliability. 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 (Preparation of calcined flour) Calcined powder of the main phase containing an alkali niobate perovskite-type oxide and calcined powder of the secondary phase containing an oxide containing Mn and Ti were produced. As raw materials for the main phase, necessary components were selected and weighed from K2CO3, Na2CO3, Nb2O5, TiO2, ZrO2, MnCO3, BaCO3, and Sc2O3 powders so that in the above composition formula (2), a1=0.48, a2=0.49, a3=0, b1=0.03, b2=0, b3=0, c=1.00, d1=0.90, d2=0.03, d3=0.03, d4=0.03, and d5=0.01. Ethanol was added to the weighed raw material powders and wet-mixed for 15 hours using a φ3 mm Zr boulder in a ball mill to obtain a slurry. The obtained slurry was dried. The dried mixed powder was calcined at 900°C for 5 hours under an atmospheric atmosphere to obtain the calcined powder of the main phase. As raw materials for the secondary phase, the necessary materials were selected and weighed from among MnCO3, TiO2, and Sc2O3 powders. MnTi2O4 was used as the oxide containing Mn and Ti. Ethanol was added to the weighed raw material powders and wet-mixed in a ball mill for 15 hours to obtain a slurry. The obtained slurry was dried. The dried mixed powder was calcined at 1300°C for 5 hours under an atmospheric atmosphere to obtain the calcined powder of the secondary phase.

[0064] (Fabrication of laminates) To the obtained calcined main phase, 1.5% by volume of calcined secondary phase was added, and a dispersant, binder, and toluene were added. A slurry was obtained by ball milling using φ3 mm Zr pebbles. Subsequently, a ceramic green sheet was fabricated by processing it into a sheet shape using the doctor blade method.

[0065] Next, a conductive paste for internal electrodes, made of Ni, was applied to a ceramic green sheet using screen printing. Multiple ceramic green sheets with the conductive paste printed on them were stacked and heat-pressed together so that the conductive paste was exposed alternately from both sides. The inert layers 12 were laminated so that they were located on the top and bottom of the laminate 90. The thickness of each inert layer 12 was approximately 100 μm. The thickness of each active layer 14 was approximately 50 μm. The thickness of each internal electrode 20 was approximately 2 μm. There were 10 layers of active layer 14. After that, the laminate 90 was obtained by cutting it into pieces with a depth of 8 mm and a width of 8 mm.

[0066] The resulting laminate 90 was held at 300°C for 5 hours in an N2 atmosphere to remove the binder. The laminate 90 after the binder removal treatment was placed in an alumina setter and subjected to a maximum temperature of 1000°C to 1070°C and an oxygen partial pressure of 10°C. -12 The samples were fired in a reducing atmosphere of atm% for 5 hours. The number of pores formed was controlled by adjusting the heating rate from 600°C during firing. A slower heating rate during firing tended to result in fewer pores being formed. Specifically, the heating time to 600°C was set to 50°C / hour, and the heating rate from 600°C was adjusted within the range of 100°C / hour to 1000°C / hour. Subsequently, the samples were annealed at 800°C for 10 hours in an N2 atmosphere.

[0067] After polishing the sides of the resulting fired laminate 90, external electrodes 30 made of Au were formed on both sides by sputtering, and then the piezoelectric elements 100 of samples 1 to 8 were obtained by polarization treatment for 10 minutes under conditions of a DC voltage of 4 kV / mm and a temperature of 50°C.

[0068] 2.Measurement method For the piezoelectric elements 100 of samples 1 to 8, the piezoelectric ceramic layer 10 is 100 μm 2 The number of pores formed in each area was determined. Furthermore, the insulation degradation time was determined by conducting high-temperature, high-electric-field insulation degradation tests. The S / E ratio was also determined by measuring the displacement when an electric field was applied.

[0069] (1) Measurement of stomata Secondary electron images were acquired from the cross-section of the ion-milled sample using a scanning electron microscope (SEM) at an acceleration voltage of 5.0 kV and a magnification of 10,000x. The imaging area was a 10 μm × 10 μm range centered on the central position (width 4 mm, thickness 15 μm along the stacking direction D1) of the 1st, 5th, and 10th layers of the active layer 14. Image analysis was performed on the extracted images using image processing software. ImageJ, an open-source image processing software, was used for image analysis. In the image analysis, the actual size of the image obtained by the above method was first input into ImageJ, then Gaussian blurring (radius 2 pixels) was performed, and the threshold for binarization was determined using the Huang method. By performing binarization, the ceramic portion was made black and the pore portion was made white to clearly distinguish between the two. For the binarized image, pores with an equivalent circle radius of 50 nm or more were defined as 100 μm. 2 The number of pores formed per 100 μm was calculated. 2 The number of pores formed per 100 μm is in the 1st, 5th, and 10th layers of the active layer 14. 2 This was calculated as the average number of stomata per unit area.

[0070] (2) High temperature / high field insulation degradation test Each sample was placed in a 130°C constant temperature bath, and its insulation resistance was measured while applying a DC electric field of 5 kV / mm. The insulation resistance value measured 1 minute after the application of the electric field was taken as the initial value. The time it took for the insulation resistance value to decrease by one order of magnitude from the initial value after the application of the electric field was defined as the degradation time (hr). For evaluation of high-temperature durability, a degradation time of 24 hours or more was classified as A, 15 hours or more but less than 24 hours as B, 5 hours or more but less than 15 hours as C, and less than 5 hours as D.

[0071] (3) Measurement of S / E Using a laser Doppler vibrometer, unipolar drive, specifically, the maximum electric field E maxA positive electric field of +3kV / mm was applied to the sample as a sine wave with a frequency of 1Hz at room temperature, 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 classified as A, 150 or more and less than 200 as B, and 100 or more and less than 150 as C.

[0072] 3.Results The results are shown in Table 1 below.

[0073] [Table 1]

[0074] The number of stomata is 100 μm. 2 Samples 1-7, each with 50 or fewer pores, showed excellent high-temperature durability, with high-temperature and high-electric-field insulation degradation times exceeding 5 hours in all cases. In particular, samples 1-3 showed minimal resistance degradation even after 24 hours. (Pore count: 100 μm) 2 Sample 8, which had 69 particles per sample, deteriorated rapidly and exhibited poor high-temperature durability. All samples had an S / E value of 100 or higher, indicating good displacement characteristics.

[0075] 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]

[0076] 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 a base metal, stacked alternately, The number of pores formed in the piezoelectric ceramic layer is 100 μm. ２ There are 50 or fewer per person. A piezoelectric element characterized by the following features.

2. In the piezoelectric element according to claim 1, The number of pores formed in the piezoelectric ceramic layer is 100 μm. ２ The number is between 3 and 50. A piezoelectric element characterized by the following features.

3. 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.

4. 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.

5. A component comprising a piezoelectric element according to any one of claims 1 to 4.

6. An apparatus comprising the component described in claim 5.

7. The apparatus according to claim 6, which is one of an actuator, a haptic, a buzzer, and an ultrasonic sensor.

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