JP2013128006A - Method for manufacturing piezoelectric/electrostrictive material film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a piezoelectric/electrostrictive material film which includes tetragonal perovskite and is high in piezoelectric/electrostrictive property, and which has an intended composition while the diffusion of lithium into a substrate is suppressed efficiently.SOLUTION: The method for manufacturing a piezoelectric/electrostrictive material film 122 including tetragonal perovskite comprises the steps of: preliminarily baking a powdery raw material having a basic composition expressed by a general formula of ABO(0.90≤x≤1.20), where A site includes Li, Na and K, and B site includes Nb, to form a preliminarily-baked material including tetragonal perovskite; pulverizing the preliminarily-baked material to prepare preliminarily-baked and pulverized powder; forming a coating film including the preliminarily-baked and pulverized powder on a substrate 11 and an electrode layer 121; and baking the coating film.

Description

  The present invention relates to a method for manufacturing a piezoelectric / electrostrictive film.

  Piezoelectric / electrostrictive actuators have the advantage that displacement can be precisely controlled on the order of submicrons. In particular, a piezoelectric / electrostrictive actuator using a sintered body of a piezoelectric / electrostrictive porcelain composition as a piezoelectric / electrostrictive body can precisely control displacement, and has high electromechanical conversion efficiency. There are also advantages such as high power, fast response speed, high durability, and low power consumption. Taking advantage of these advantages, they are employed in inkjet printer heads, diesel engine injectors, and the like.

  Conventionally, lead zirconate titanate (PZT) -based compositions have been used as piezoelectric / electrostrictive porcelain compositions for piezoelectric / electrostrictive actuators. However, although PZT has high strain characteristics, it contains lead, which is a harmful substance, and therefore, the influence of elution of lead from the sintered body on the global environment has been strongly concerned.

Thus, in recent years, alkali niobate-based piezoelectric / electrostrictive porcelain compositions have been proposed. For example, in Patent Document 1, the composition formula is Li _x (K _1-y Na _y ) _1-x (Nb _1-z Ta _z ) O ₃ (however, 0.001 ≦ x ≦ 0.2, 0 ≦ y An alkali metal-containing niobium oxide piezoelectric material composition comprising a solid solution represented by ≦ 0.8 and 0 <z ≦ 0.4) is disclosed. Patent Document 2 includes a general formula: {Li _x (K _1−y Na _y ) _1−x } {Nb _1−z−w Ta _z Sb _w } O ₃ (where 0 ≦ x ≦ 0.2, 0 ≦ y ≦ 1, 0 ≦ z ≦ 0.4, 0 ≦ w ≦ 0.2, x + z + w> 0), and a polycrystal having an isotropic perovskite compound as a main phase. A crystal-oriented ceramic in which specific crystal planes of crystal grains constituting a crystal body are oriented is disclosed. Non-Patent Document 1 discloses that a (Li, Na, K) (Nb, Ta) O ₃ piezoelectric material achieves piezoelectric characteristics comparable to PZT while being non-lead. Non-Patent Document 2 describes a lead-free high-temperature piezoelectric ceramic having good [Li _x (Na _0.5 K _0.5 ) _1-x ] NbO ₃ (0.04 ≦ x ≦ 0.20) to which lithium is added. It is disclosed that there is. All of the bodies disclosed in these documents are in bulk form.

On the other hand, a piezoelectric thin film element using a film-shaped body is also known. For example, in Patent Document 3, in a piezoelectric thin film element in which a lower electrode, a piezoelectric thin film, and an upper electrode are arranged on a substrate, the piezoelectric thin film is (Na _x1 K _y1 Li _z1 ) NbO ₃ (0 <x1 <1, 0. 4 <y1 <1, 0 ≦ z1 <1, x1 + y1 + z1 = 1), which is a dielectric thin film having an alkali niobium oxide perovskite structure, and (Na _x2 K _y2 Li between the lower electrode and the piezoelectric thin film) _z2 ) an underlayer dielectric thin film of an alkali niobium oxide perovskite structure represented by NbO ₃ (0 <x2 <1, 0 <y2 ≦ 0.4, 0 ≦ z2 <1, x2 + y2 + z2 = 1 and y1> y2) A piezoelectric thin film element is disclosed.

Japanese Patent No. 3531803 Japanese Patent No. 4326374 Japanese Patent No. 4258530

Y. Saito et.al., Nature 432, 84-87 (2004) Y. Guo et al., App. Phys. Lett. 85 (2004) 4121

However, a piezoelectric film type element obtained by forming a (Li, Na, K) (Nb, Ta) O ₃ -based non-lead piezoelectric material into a film cannot sufficiently exhibit the inherent properties of the material. This is because, during firing, lithium passes through the lower electrode (eg, platinum film) and diffuses into the substrate (eg, zirconium oxide), resulting in (Li, Na, K) (Nb, Ta) O ₃ -based lead-free piezoelectric. This is probably because the lithium concentration in the body membrane is significantly reduced. That is, lithium is an element necessary for making a (Li, Na, K) (Nb, Ta) O ₃ -based non-lead piezoelectric body into a tetragonal crystal having high piezoelectric characteristics. And the like, the lithium concentration of the (Li, Na, K) (Nb, Ta) O ₃ -based non-lead piezoelectric film is reduced to form orthorhombic crystals with low characteristics. Conceivable. For this reason, it is considered that the performance of the piezoelectric element formed into a film is lower than the characteristics expected from the initial charged composition.

  The inventors of the present invention effectively diffused lithium into the substrate by forming a tetragonal perovskite substantially free of different phases when calcining the raw material powder for the piezoelectric / electrostrictive film. It was found that a piezoelectric / electrostrictive film having high characteristics made of tetragonal perovskite having the desired composition can be produced.

  Accordingly, an object of the present invention is to effectively prevent the diffusion of lithium to the substrate, and to obtain a piezoelectric / electrostrictive film having a high characteristic of tetragonal perovskite having a target composition and no lack of lithium. An object of the present invention is to provide a method for producing an electrostrictive film and a powder composition used for the production.

According to one embodiment of the present invention, it is represented by the general formula A _x BO _{3 ± δ} (where 0.90 ≦ x ≦ 1.20, δ represents an oxygen excess or oxygen deficiency, but may be 0). A method for producing a piezoelectric / electrostrictive film comprising a tetragonal perovskite having a basic composition in which an A site contains Li, Na, and K and a B site contains Nb,
Preparing a raw material powder having the basic composition;
Calcination of the raw material powder to form a calcined product of tetragonal perovskite;
Crushing the calcined product to obtain a calcined / pulverized powder;
Forming a film containing the calcined / ground powder on a substrate;
And baking the coating to form a piezoelectric / electrostrictive film made of tetragonal perovskite.

FIG. 3 is a schematic cross-sectional view of a single layer type piezoelectric / electrostrictive actuator. It is a schematic cross section of a modification of the piezoelectric / electrostrictive actuator shown in FIG. 1A. It is a schematic cross section of a multilayer type piezoelectric / electrostrictive actuator. It is a schematic cross section of a modification of the piezoelectric / electrostrictive actuator shown in FIG. 2A. It is a schematic cross section of a multilayer type piezoelectric / electrostrictive actuator. FIG. 3B is a schematic cross-sectional view of a modified example of the piezoelectric / electrostrictive actuator shown in FIG. 3A.

Method for Manufacturing Piezoelectric / Electrostrictive Film The method according to the present invention has a general formula A _x BO _{3 ± δ} (where 0.90 ≦ x ≦ 1.20, δ represents an oxygen excess amount or an oxygen deficiency amount, but 0 The piezoelectric / electrostrictive film is made of tetragonal perovskite having a basic composition in which the A site contains Li, Na, and K and the B site contains Nb. The basic composition represented by this general formula includes both stoichiometric and non-stoichiometric compositions. However, even with the latest equipment, oxygen excess or oxygen deficiency (δ) can be analyzed and in light of the circumstances that can not be quantified, but that may be abbreviated as customary a _x BO _3. In any case, it is considered that there is no problem if 0 ≦ δ <1. Thus, the piezoelectric / electrostrictive film of the present invention has a (Li, Na, K) (Nb) O ₃ -based stoichiometric composition and non-stoichiometric composition, and the square of such a composition. By producing a piezoelectric / electrostrictive film made of crystal perovskite according to the target composition, excellent piezoelectric / electrostrictive characteristics can be exhibited while being lead-free.

  In the above general formula, the A site may further contain at least one A site substitution element selected from the group consisting of Bi, Ba, Sr, Ca, La, Ce, Nd, Sm, Dy, Ho, Yb, and Ag. Good. These A site substitution elements preferably occupy 0.5 atomic percent or less of all atoms constituting the A site, more preferably 0.2 atomic percent or less, and even more preferably 0.1 atomic percent or less. is there.

  In the above general formula, the B site may further contain at least one B site substitution element selected from the group consisting of Ta, Sb, Ti, Zr, V, Cr, Fe, Co, Ni, and Cu, and more preferably. Is a combination of Ta and Sb. These B site substitution elements preferably occupy 50 atomic percent or less of all atoms constituting the B site, more preferably 25 atomic percent or less, and even more preferably 15 atomic percent or less.

In the above general formula, the ratio x of the atoms constituting the A site to the atoms constituting the B site is 0.90 ≦ x ≦ 1.20, but preferably 1 ≦ x ≦ 1.20. Preferably 1 <x ≦ 1.05. As described above, when the atoms constituting the A site are richer than the atoms constituting the B site, high piezoelectric / electrostrictive characteristics are easily obtained, but the stoichiometric composition is caused by excess alkali metal. It is easier to produce a heterogeneous phase (particularly LiNbO ₃ ), and the alkali element is more likely to diffuse into the substrate. In this regard, according to the method of the present invention, when a raw material powder for a piezoelectric / electrostrictive film is calcined, a tetragonal perovskite having substantially no heterogeneous phase is formed, thereby diffusing alkali elements into the substrate. Can be effectively prevented, and a piezoelectric / electrostrictive film made of tetragonal perovskite having a desired composition can be manufactured.

  The piezoelectric / electrostrictive film may further include at least one selected from the group consisting of Mn and Zn. Both Mn and Zn do not form a solid solution at the B site of the perovskite but tend to be contained in the different phase or grain boundary phase, but may be contained in any part of the film.

Preparation of Raw Material Powder In the method of the present invention, first, a raw material powder having the basic composition of the piezoelectric / electrostrictive film to be finally obtained is prepared. The raw material powder is produced by adding a dispersion medium to the raw material powder of the constituent elements of the perovskite oxide (Li, Na, K, Nb, Ta, Sb, etc.), and then adding the raw material powder to which the dispersion medium is added to the mortar What is necessary is just to mix and mix by pot mills, such as a ball mill, bead mill, a hammer mill, a jet mill. As the raw material of the constituent element of the perovskite oxide, an oxide or a compound such as carbonate or tartrate that becomes an oxide in the calcination process can be used. As the dispersion medium, an organic solvent such as ethanol, toluene, or acetone can be used. The dispersion medium is removed from the mixed slurry thus obtained by evaporation drying, filtration or the like, and a dried raw material powder is obtained.

  The dried raw material powder may be pre-calcined at a temperature of 600 to 900 ° C. By performing preliminary calcination before calcination, there is a tendency that the uniformity of the elements becomes high or an extra foreign phase tends to disappear, which can contribute to improvement of characteristics. The preliminary calcination may be performed only once or may be performed twice or more. When two or more preliminary calcinations are performed, the conditions of each preliminary calcination may be the same or different. The atmosphere at the time of preliminary calcination may be an air atmosphere or an oxygen atmosphere. The temperature increase rate and temperature decrease rate during the preliminary calcination are desirably 20 to 2000 ° C./hour, and the time for maintaining the preliminary calcination temperature is desirably 30 seconds to 20 hours. In order to obtain preliminarily calcined / pulverized powder having a desired particle size, pulverization may be performed by a ball mill or the like after the precalcination. When pulverization is performed, pulverization methods such as mortar pulverization, pot mill, bead mill, hammer mill, jet mill, mesh or screen pressing are used.

Formation and pulverization of tetragonal perovskite calcined material powder or preliminary calcined material is calcined to form a calcined product of tetragonal perovskite. Thereby, lithium can be sufficiently dissolved in the perovskite to substantially eliminate the heterogeneous phase. Accordingly, this calcined product is preferably composed of a single phase of tetragonal perovskite, but it is acceptable to include a crystal phase having an impurity level of less than 5% by weight, preferably less than 2% by weight, more preferably less than 1% by weight. The

As described above, lithium is an element necessary for making a (Li, Na, K) (Nb, Ta) O ₃ -based non-lead piezoelectric material into a tetragonal crystal having high piezoelectric characteristics. By diffusing into the substrate through the grain boundaries, etc., the lithium concentration of the (Li, Na, K) (Nb, Ta) O ₃ -based non-lead piezoelectric film is lowered, resulting in an orthorhombic crystal having low characteristics. It is considered a thing. Such diffusion of lithium into the substrate is likely to occur particularly when LiNbO ₃ is included as a different phase. In order to prevent the occurrence of a heterogeneous phase in which lithium is liable to diffuse into the substrate, a tetragonal perovskite having substantially no heterogeneous phase is formed when the raw material powder for piezoelectric / electrostrictive film is calcined. It is effective to sufficiently dissolve lithium in the perovskite during calcination.

That is, according to a known method, the piezoelectric powder raw material before filming is produced by mixing raw materials, calcining and pulverization, but this leads to contamination during pulverization leading to performance degradation and insufficient densification. In order to avoid the coarsening of the particle size, calcination at a high temperature is not performed. As a result, the piezoelectric raw material powder is not a perovskite single phase, and LiNbO _{3 that} is liable to preferentially diffuse lithium into the substrate (particularly the zirconium oxide substrate) during film firing is generated as a different phase. However, the method of the present invention is a tetragonal crystal having substantially no heterogeneous phase while appropriately performing temperature control during calcination as desired so as to minimize or avoid the above-mentioned problems associated with calcination at high temperatures. Rather, it is based on the new knowledge that the positive formation of the calcined material made of perovskite is much more beneficial in improving the characteristics of the piezoelectric / electrostrictive film.

  According to a preferred embodiment of the present invention, the calcining is performed by heating the raw material powder at a temperature rising rate of 200 to 2000 ° C./h to a temperature of 900 to 1200 ° C. and holding at this temperature for 0 to 10 minutes. It is performed according to a temperature profile including cooling to 800 ° C. at a rate of temperature decrease of 200 to 2000 ° C./h. At that time, in the temperature profile, it is preferable that the temperature operation is performed so that the temperature time area calculated by multiplying the temperature by time in the temperature region of 800 ° C. or higher is 67 to 200 ° C. · h, more preferably. Is 67 to 155 ° C · h. Here, the holding time of 0 hours does not mean that the calcination is not performed, but means that the temperature is raised immediately and then cooled immediately after reaching a predetermined temperature. Within the range of such temperature operating conditions, the calcined product can be reliably obtained as tetragonal crystals having substantially no heterogeneous phase, and sintering and grain growth that make pulverization difficult can be avoided. This facilitates pulverization in the subsequent process and improves the sinterability of the calcined / pulverized powder. As a result, the relative density of the piezoelectric / electrostrictive film increases and the characteristics of the piezoelectric / electrostrictive film are improved. Can do.

  The calcination may be performed only once or may be performed twice or more. When two or more calcinations are performed, the conditions for each calcination may be the same or different. The atmosphere at the time of calcination may be an air atmosphere or an oxygen atmosphere.

  The obtained calcined product is pulverized by a ball mill or the like to be calcined / pulverized powder. Thereby, a particle size can be made small and a specific surface area can be enlarged, and the sinterability at the time of film formation can be improved. The pulverization may be performed by mortar pulverization, pot mill, bead mill, hammer mill, jet mill, mesh or screen pressing method.

  The volume standard D50 (median diameter) of the calcined / ground powder is preferably 0.07 to 10 μm, and more preferably 0.1 to 3 μm. Further, the calcined / ground powder may be heat treated at 400 to 850 ° C. in order to adjust the particle size of the calcined / ground powder. Since finer particles are easier to be integrated with other particles, by performing this heat treatment, a calcined / ground powder having a uniform particle size is obtained, and a sintered body having a uniform particle size is obtained.

Production of Piezoelectric / Electrostrictive Film A film containing the obtained calcined / ground powder is formed on the substrate. This film can be formed by various film forming methods that can use powder. The substrate on which the film is formed preferably includes an inorganic oxide base material and a lower electrode layer formed on the inorganic oxide base material, and a piezoelectric / electrostrictive film is formed on the lower electrode layer. It is formed. Further, before firing, a step of forming an intermediate electrode layer on the film containing the calcined / ground powder and further forming a film containing the calcined / ground powder on the intermediate electrode layer may be performed. Can be performed once or multiple times. An upper electrode layer may be further formed on the piezoelectric / electrostrictive film as the uppermost layer in the same manner as the intermediate electrode layer.

  The film thus formed is baked to form a piezoelectric / electrostrictive film made of tetragonal perovskite. This piezoelectric / electrostrictive film is preferably composed of a single phase of tetragonal perovskite, but also includes a crystal phase having an impurity level of less than 5% by weight, preferably less than 2% by weight, more preferably less than 1% by weight. Permissible. Since the piezoelectric / electrostrictive film thus obtained is composed of tetragonal perovskite, it exhibits high piezoelectric characteristics, and a piezoelectric / electrostrictive element such as a piezoelectric / electrostrictive actuator having high piezoelectric / electrostrictive characteristics is realized. Can do.

  Hereinafter, the manufacturing process of the piezoelectric / electrostrictive film will be described based on specific embodiments of the piezoelectric / electrostrictive actuator including the piezoelectric / electrostrictive film manufactured according to the present invention. It is not limited to the specific embodiment.

  FIG. 1A shows a schematic cross-sectional view of a single-layer piezoelectric / electrostrictive actuator 1. As shown in FIG. 1A, the piezoelectric / electrostrictive actuator 1 has a structure in which an electrode layer 121, a piezoelectric / electrostrictive film 122, and an electrode layer 123 are laminated on the upper surface of a substrate 11 in this order. The electrode layers 121 and 123 on both main surfaces of the piezoelectric / electrostrictive film 122 face each other with the piezoelectric / electrostrictive film 122 interposed therebetween. The laminate 12 in which the electrode layer 121, the piezoelectric / electrostrictive film 122 and the electrode layer 123 are laminated is fixed to the substrate 11. “Fixing” refers to bonding the laminate 12 to the substrate 11 by a solid phase reaction at the interface between the substrate 11 and the laminate 12 without using an organic adhesive or an inorganic adhesive. Note that the laminate may be bonded to the substrate by a solid phase reaction at the interface between the substrate and the piezoelectric / electrostrictive film at the bottom layer of the laminate. In the piezoelectric / electrostrictive actuator 1, when a voltage is applied to the electrode layers 121 and 123, the piezoelectric / electrostrictive body 122 expands and contracts in a direction perpendicular to the electric field according to the applied voltage, and as a result, bending displacement occurs. Arise.

  The piezoelectric / electrostrictive film 122 is a film made of tetragonal perovskite obtained by the production method of the present invention. The film thickness of the piezoelectric / electrostrictive film 122 is preferably 0.5 to 50 μm, more preferably 0.8 to 40 μm, and particularly preferably 1 to 30 μm. When the film thickness is in such a range, sufficient densification can be obtained, and the shrinkage stress during sintering does not become too large. Therefore, the thickness of the substrate 11 can be reduced to reduce the thickness of the piezoelectric / electrostrictive actuator 1. Miniaturization can be realized.

  The material of the electrode layers 121 and 123 is a metal such as platinum, palladium, rhodium, gold or silver, or an alloy thereof. Among these, platinum or an alloy containing platinum as a main component is preferable in terms of high heat resistance during firing. Depending on the firing temperature, an alloy such as silver-palladium is also preferably used. The film thicknesses of the electrode layers 121 and 123 are preferably 15 μm or less, and more preferably 5 μm or less. When the film thickness is in such a range, the electrode layers 121 and 123 can be prevented from functioning as a relaxation layer, and a large bending displacement can be secured. In addition, in order for the electrode layers 121 and 123 to appropriately perform their roles, the film thickness of the electrode layers 121 and 123 is preferably 0.05 μm or more. The electrode layers 121 and 123 are preferably formed so as to cover regions that substantially contribute to the bending displacement of the piezoelectric / electrostrictive film 122. For example, the piezoelectric / electrostrictive film 122 is preferably formed so as to cover a region including 80% or more of both main surfaces of the piezoelectric / electrostrictive film 122 including the central portion.

  Although the material of the board | substrate 11 is ceramics, there is no restriction | limiting in the kind. However, ceramics including at least one selected from the group consisting of stabilized zirconium oxide, aluminum oxide, magnesium oxide, mullite, aluminum nitride, silicon nitride and glass from the viewpoints of heat resistance, chemical stability, and insulation. It is preferable that Among these, stabilized zirconium oxide is more preferable from the viewpoint of mechanical strength and toughness. “Stabilized zirconium oxide” refers to zirconium oxide in which the phase transition of the crystal is suppressed by the addition of a stabilizer, and includes partially stabilized zirconium oxide in addition to stabilized zirconium oxide.

  Examples of the stabilized zirconium oxide include zirconium oxide containing 1 to 30 mol% of calcium oxide, magnesium oxide, yttrium oxide, ytterbium oxide, cerium oxide, or a rare earth metal oxide as a stabilizer. Of these, zirconium oxide containing yttrium oxide as a stabilizer is preferred because of its particularly high mechanical strength. The content of yttrium oxide is preferably 1.5 to 6 mol%, and more preferably 2 to 4 mol%. In addition to yttrium oxide, it is more preferable to contain 0.1 to 5 mol% of aluminum oxide. The stabilized zirconium oxide crystal phase is a mixed crystal of cubic and monoclinic, a mixed crystal of tetragonal and monoclinic, or a mixed crystal of cubic, tetragonal and monoclinic, etc. However, it is preferable from the viewpoint of mechanical strength, toughness, and durability that the main crystal phase is a mixed crystal of tetragonal crystals and cubic crystals or a tetragonal crystal.

  The thickness of the substrate 11 is uniform. The thickness of the substrate 11 is preferably 1 to 1000 μm, more preferably 1.5 to 500 μm, and particularly preferably 2 to 200 μm. When the plate thickness is in such a range, high mechanical strength of the piezoelectric / electrostrictive actuator 1 can be secured, and the rigidity of the substrate 11 is prevented from becoming too high, and the piezoelectric / electrostrictive film at the time of voltage application is prevented. The bending displacement due to the expansion and contraction of 122 can be increased. The surface shape of the substrate 11 (the shape of the surface to which the laminate is fixed) is not particularly limited, and can be a triangle, a rectangle (rectangle or square), an ellipse, or a circle. You may go. It is good also as a compound form which combined these basic forms.

  In manufacturing the piezoelectric / electrostrictive actuator 1, the electrode layer 121 is formed on the substrate 11. The electrode layer 121 is formed by a method such as ion beam, sputtering, vacuum deposition, PVD (Physical Vapor Deposition), ion plating, CVD (Chemical Vapor Deposition), plating, aerosol deposition, screen printing, spraying, dipping, or the like. . Among these, from the viewpoint of bonding properties with the substrate 11 and the piezoelectric / electrostrictive film 122, a sputtering method or a screen printing method is preferable. The formed electrode layer 121 is fixed to the substrate 11 and the piezoelectric / electrostrictive film 122 by heat treatment. The temperature of the heat treatment is approximately 500 to 1400 ° C., although it varies depending on the material of the electrode layer 121 and the formation method.

  Subsequently, the piezoelectric / electrostrictive film 122 is formed on the electrode layer 121 using the calcined / ground powder according to the present invention. Piezoelectric / electrostrictive film 122 includes ion beam, sputtering, vacuum deposition, PVD (Physical Vapor Deposition), ion plating, CVD (Chemical Vapor Deposition), plating, sol-gel, aerosol deposition, screen printing, spraying, dipping, etc. It is formed by the method. Among them, the screen printing method is preferable in that the accuracy of the planar shape and the film thickness is high and the piezoelectric / electrostrictive film can be continuously formed. Subsequently, an electrode layer 123 is formed on the piezoelectric / electrostrictive film 122. The electrode layer 123 is formed in the same manner as the electrode layer 121.

  After forming the electrode layer 123, the substrate 11 on which the laminate 12 is formed is integrally fired. By this firing, the piezoelectric / electrostrictive film 122 is sintered, and the electrode layers 121 and 123 are heat-treated. The firing temperature of the piezoelectric / electrostrictive film 122 is preferably 800 to 1250 ° C, and more preferably 900 to 1200 ° C. When the temperature is in such a range, the piezoelectric / electrostrictive film 122 is sufficiently densified, and the substrate 11 and the electrode layer 121 are fixed, and the electrode layers 121 and 123 and the piezoelectric / electrostrictive film 122 are fixed. And a high piezoelectric / electrostrictive characteristic can be realized. Further, the maximum temperature holding time during firing is preferably 0 to 20 hours, more preferably 1 minute to 10 hours, and further preferably 5 minutes to 4 hours. Within this range, the piezoelectric / electrostrictive film 122 can be sufficiently densified and high piezoelectric / electrostrictive characteristics can be realized. Here, the holding time of 0 hour does not mean that the firing is not performed, but means that the temperature is raised and reaches a predetermined temperature, and then immediately cooled.

  Note that the heat treatment of the electrode layers 121 and 123 is preferably performed together with the firing from the viewpoint of productivity, but this does not prevent the heat treatment from being performed every time the electrode layers 121 and 123 are formed. However, when the piezoelectric / electrostrictive film 122 is fired before the heat treatment of the electrode layer 123, the electrode layer 123 is heat treated at a temperature lower than the firing temperature of the piezoelectric / electrostrictive film 122. After the completion of firing, a polarization process and an aging process are performed on the piezoelectric / electrostrictive actuator.

  The piezoelectric / electrostrictive actuator 1 is also manufactured by a green sheet laminating method that is commonly used in the production of multilayer ceramic electronic components. In the green sheet laminating method, a binder, a plasticizer, a dispersant, and a dispersion medium are added to a raw material powder, and ceramics, a binder, a plasticizer, and a dispersion medium are mixed by a ball mill or the like. The obtained slurry is formed into a sheet shape by a doctor blade method or the like to obtain a formed body.

  Subsequently, an electrode paste film is printed on both main surfaces of the molded body by a screen printing method or the like. The electrode paste used here is obtained by adding a solvent, vehicle, glass frit, or the like to the above-described metal or alloy powder. Subsequently, the molded body having the electrode paste film printed on both main surfaces and the substrate are pressure-bonded. Thereafter, the substrate on which the laminate is formed is integrally fired, and after the firing is finished, polarization treatment and aging treatment are performed under appropriate conditions.

  FIG. 1B shows a schematic cross-sectional view of a modified example of the single-layer piezoelectric / electrostrictive actuator 1. The piezoelectric / electrostrictive actuator 1 ′ shown in FIG. 1B is a single-layer type shown in FIG. 1A except that the electrode layer 121 ′ in contact with the substrate 11 ′ is formed over a wider area than the piezoelectric / electrostrictive film 122 ′. This is the same as the piezoelectric / electrostrictive actuator 1 of FIG. According to this configuration, there is an advantage that the piezoelectric / electrostrictive film 122 ′ is less likely to contact the substrate 11 ′, and as a result, diffusion of lithium to the substrate 11 ′ is easily suppressed.

  FIG. 2A shows a schematic cross-sectional view of the multilayer piezoelectric / electrostrictive actuator 2. As shown in FIG. 2A, the piezoelectric / electrostrictive actuator 2 includes an electrode layer 221, a piezoelectric / electrostrictive film 222, an electrode layer 223, a piezoelectric / electrostrictive film 224, and an electrode layer 225 on the upper surface of the substrate 21. It has a structure laminated in this order. The electrode layers 221 and 223 on both main surfaces of the piezoelectric / electrostrictive film 222 face each other with the piezoelectric / electrostrictive film 222 interposed therebetween, and the electrode layers 223 and 223 on both main surfaces of the piezoelectric / electrostrictive film 224 are opposed to each other. 225 opposes with the piezoelectric / electrostrictive film 224 interposed therebetween. The laminate 22 in which the electrode layer 221, the piezoelectric / electrostrictive film 222, the electrode layer 223, the piezoelectric / electrostrictive film 224 and the electrode layer 225 are laminated is fixed to the substrate 21. 2A shows a case where the piezoelectric / electrostrictive film has two layers, the piezoelectric / electrostrictive film may have three or more layers. As for the thickness of the substrate 21 of the piezoelectric / electrostrictive actuator 2, the central portion 215 to which the laminated body 22 is bonded is thinner than the peripheral portion 216. Thereby, the bending displacement can be increased while maintaining the mechanical strength of the substrate 21. The substrate 21 may be used for the piezoelectric / electrostrictive actuator 1 of the second embodiment. The piezoelectric / electrostrictive actuator 2 is also manufactured in the same manner as the single-layer piezoelectric / electrostrictive actuator 1 except that the number of piezoelectric / electrostrictive films and electrode layers to be formed is increased.

  FIG. 2B shows a schematic cross-sectional view of a modified example of the multilayer piezoelectric / electrostrictive actuator 2. The piezoelectric / electrostrictive actuator 2 ′ shown in FIG. 2B is the multilayer type shown in FIG. 2A except that the electrode layer 221 ′ in contact with the substrate 21 ′ is formed over a wider area than the piezoelectric / electrostrictive film 222 ′. Similar to the piezoelectric / electrostrictive actuator 2. According to this configuration, there is an advantage that the piezoelectric / electrostrictive film 222 ′ is not easily in contact with the substrate 21 ′, and as a result, diffusion of lithium to the substrate 21 ′ is easily suppressed.

  FIG. 3A shows a schematic cross-sectional view of the multilayer piezoelectric / electrostrictive actuator 3. As shown in FIG. 3A, the piezoelectric / electrostrictive actuator 3 includes a substrate 31 on which a unit structure having the same structure as the substrate 21 of the third embodiment is repeated. On each of the unit structures of the substrate 31, a laminate 32 having the same structure as the laminate 22 of the third embodiment is fixed. The piezoelectric / electrostrictive actuator 3 is also manufactured in the same manner as the single-layer piezoelectric / electrostrictive actuator 1 except that the number of laminated bodies to be formed and the number of piezoelectric / electrostrictive films and electrode layers are increased. The

  FIG. 3B shows a schematic cross-sectional view of a modified example of the multilayer piezoelectric / electrostrictive actuator 3. The piezoelectric / electrostrictive actuator 3 ′ shown in FIG. 3B is the multilayer type shown in FIG. 3A except that the electrode layer 321 ′ in contact with the substrate 31 ′ is formed over a wider area than the piezoelectric / electrostrictive film 322 ′. The same as the piezoelectric / electrostrictive actuator 3. According to this configuration, there is an advantage that the piezoelectric / electrostrictive film 322 'is unlikely to contact the substrate 31', and as a result, diffusion of lithium to the substrate 31 'is easily suppressed.

  The invention is further illustrated by the following examples.

Example 1: Production of Piezoelectric / Electrostrictive Film and Piezoelectric / Electrostrictive Actuator Production of piezoelectric / electrostrictive films having various target compositions shown in Samples 2, 4, 6 to 10 and 12 in Tables 1 to 4 The following procedure was followed according to the method of the invention. For comparison, as samples 1, 3, 5 and 11, production of piezoelectric / electrostrictive films having various target compositions was also attempted by a method not following the method of the present invention.

(1) Preparation of perovskite calcined / ground powder Lithium carbonate (Li ₂ CO ₃ ), sodium hydrogen tartrate monohydrate (C ₄ H ₅ O ₆ Na.H ₂ O), potassium hydrogen tartrate (C ₄ H ₅ O ₆ K), raw material powders of niobium oxide (Nb ₂ O ₅ ) and tantalum oxide (Ta ₂ O ₅ ) were weighed so as to have the target composition shown in Tables 1 to 4 in the oxide after firing. . Subsequently, alcohol was added as a dispersion medium to the weighed raw material powders and mixed for 16 hours by a ball mill. Subsequently, the obtained mixed raw material was dried, preliminarily calcined at 800 ° C. for 5 hours, and pulverized by a ball mill to obtain a pulverized powder of a preliminarily calcined product. This preliminary calcination corresponds to the main calcination in the conventional method. For comparison, only the preliminary calcination was performed on samples 1, 3, 5 and 11, and the subsequent calcination was not performed. On the other hand, for samples 2, 4, 6 to 10 and 12, the preliminary calcined / ground powder was further calcined according to the calcining conditions shown in Tables 1 to 4 and pulverized with a ball mill to obtain a calcined ground powder. Got. Subsequently, the pulverized powder was passed through a 100 mesh sieve to adjust the particle size. The specific surface area of the calcined product before pulverization and the specific surface area of the calcined product after pulverization were measured by a trade name “Flowsorb III2305” (manufactured by Shimadzu Corporation). Thus, a perovskite calcined / ground powder was obtained.

The X-ray diffraction pattern of the calcined / ground powder obtained was measured with an X-ray diffractometer (Bulker AXS, D8ADVANCE) under the following conditions, and subjected to Rietveld analysis (analysis software: Bruker AXS, TOPAS). Thus, the crystal structure and the amount of different phases contained in the calcined / ground powder were analyzed.
-X-ray output: 40 kV x 40 mA
-Goniometer radius: 250mm
-Divergent slit: 0.6 °
-Scattering slit: 0.6 °
-Light receiving slit: 0.2mm
-Solar slit: 4 ° (incident side, light receiving side)
-Measurement method: 2θ / θ method using a sample horizontal type concentrated optical system (2θ = 20-60 ° is measured, step width is 0.01 °)
As a result, tetragonal perovskite single phase was confirmed for Samples 2, 4, 6 to 10 and 12, while in Samples 1, 3, 5 and 11, the presence of a heterogeneous phase composed of LiNbO ₃ other than orthorhombic perovskite was confirmed. It was done.

(2) Production of Piezoelectric / Electrostrictive Actuator Using the obtained calcined / pulverized powder, a piezoelectric / electrostrictive actuator 1 ′ shown in FIG. 1B was produced. First, a platinum paste was screen-printed on a stabilized zirconium oxide substrate as the substrate 11 ′, and a platinum electrode layer 121 ′ was formed by heat treatment. Next, an unfired piezoelectric / electrostrictive film 122 ′ was formed on the platinum electrode layer 121 ′ by screen printing a paste prepared by mixing calcined / ground powder with a binder. Subsequently, a composition composed of the base material 11 ′, the platinum electrode layer 121 ′ and the unfired piezoelectric / electrostrictive film 122 ′ was housed in an alumina container and fired at 1050 ° C. for 3 hours. Subsequently, a gold paste was screen printed on the fired piezoelectric / electrostrictive film 122 ′, and a gold electrode layer 123 ′ was formed by heat treatment. Thus, a piezoelectric / electrostrictive actuator provided with a piezoelectric / electrostrictive film made of tetragonal perovskite was obtained.

Example 2: Evaluation of piezoelectric / electrostrictive film The piezoelectric / electrostrictive films of Samples 1 to 11 prepared in Example 1 were evaluated as follows.

(1) Crystal structure analysis The X-ray diffraction pattern of the fired piezoelectric / electrostrictive film element was measured with an X-ray diffractometer (Bulker AXS, D8ADVANCE) under the following conditions to analyze the crystal structure.
-X-ray output: 40 kV x 40 mA
-Goniometer radius: 250mm
-Divergent slit: 0.6 °
-Scattering slit: 0.6 °
-Light receiving slit: 0.2mm
-Solar slit: 4 ° (incident side, light receiving side)
-Measurement method: 2θ / θ method using a sample horizontal type concentrated optical system (2θ = 20-60 ° is measured, step width is 0.01 °)

(2) Surface microstructure observation After the surface of the fired piezoelectric / electrostrictive element was sputtered with an ion sputtering apparatus (JFC-1500, manufactured by JEOL Ltd.) to a thickness of about 10 nm, the surface The microstructure was observed with a scanning electron microscope (JSM-6390, manufactured by JEOL Ltd.) to obtain a secondary electron image.

(3) Cross-sectional microstructure observation and elemental analysis The piezoelectric / electrostrictive film element was mechanically polished, and the cross section of the piezoelectric / electrostrictive film element was observed with FE-EPMA (JXA-8530F, manufactured by JEOL Ltd.). The degree of densification of the film was evaluated. In addition, elemental analysis was performed to calculate the composition of elements other than lithium.

(4) Lithium concentration analysis Li-direction analysis of the piezoelectric / electrostrictive film element after firing was performed using D-SIMS (manufactured by CAMCA, IMS-6f), and the lithium concentration of the piezoelectric / electrostrictive film was Was calculated.

(5) Measurement of relative density From the cross-sectional photograph of the piezoelectric / electrostrictive film obtained in (3) above, using image editing software (trade name “Image-Pro”, manufactured by Media Cybernetics), the pore portion The relative density of the piezoelectric / electrostrictive film was evaluated.

The obtained results were as shown in Tables 1 to 4. In these tables, the crystal system of the obtained piezoelectric / electrostrictive film was determined by the above (1), the Li amount was determined by the above (4), and the obtained piezoelectric / electrostrictive film was The final composition of the electrostrictive film is determined based on the evaluation results (3) and (4) above. As can be seen from these tables, in Samples 2, 4, 6 to 10 and 12 in which a tetragonal perovskite single phase was formed during calcination, substantially no diffusion of lithium to the substrate was observed. Thus, a piezoelectric / electrostrictive film composed of tetragonal perovskite and having high characteristics as intended was obtained. On the other hand, in the samples 1, 3, 5, and 11 in which the preliminarily calcination is performed and the heterophase LiNbO ₃ is generated in addition to the orthorhombic perovskite, the rhombic is caused by the diffusion of lithium to the substrate. A piezoelectric / electrostrictive film having low characteristics made of crystalline perovskite was obtained. Samples 2, 4, 6 to 8 and 12 have calcining conditions within the range of the preferred embodiment of the present invention, and compared with samples 9 and 10 calcined under conditions outside this preferred range, The specific surface area is high and therefore the relative density is greatly increased.

As shown in Table 1, the calcined / ground powder in Sample 1 contains LiNbO ₃ in addition to orthorhombic perovskite. When this calcination / pulverized powder is used to form a bulk piezoelectric / electrostrictive body, LiNbO ₃ dissolves in the perovskite during firing, and the lithium amount of the perovskite becomes a predetermined amount. Crystalline perovskite. However, in the case of forming a film-form piezoelectric / electrostrictive body using the calcined / ground powder of Sample 1, LiNbO ₃ diffuses into the ceramic substrate during firing, and the piezoelectric / electrostrictive film The amount of Li becomes less than a predetermined amount, resulting in orthorhombic crystals with low characteristics. In this respect, according to the method of the present invention, a tetragonal crystal having high piezoelectric / electrostrictive characteristics can be obtained while being in the form of a film as shown in Sample 2 of Table 1.

1,1 ′, 2,2 ′, 3,3 ′ Piezoelectric / electrostrictive actuator 11,11 ′, 21,21 ′, 31,31 ′ Substrate 122,122 ′, 222,224,222 ′, 224 ′, 322 , 324, 322 ', 324' Piezoelectric / electrostrictive film 121, 121 ', 123, 123', 221, 221 ', 223, 223', 225, 225 ', 321, 321', 323, 323 ', 325 , 325 'electrode layer

Claims (18)

It is represented by the general formula A _x BO _{3 ± δ} (where 0.90 ≦ x ≦ 1.20, δ represents oxygen excess or oxygen deficiency, but may be 0), and the A site is Li, Na and A method for producing a piezoelectric / electrostrictive film comprising tetragonal perovskite having a basic composition containing K and containing B at a B site,
Preparing a raw material powder having the basic composition;
Calcination of the raw material powder to form a calcined product of tetragonal perovskite;
Crushing the calcined product to obtain a calcined / pulverized powder;
Forming a film containing the calcined / ground powder on a substrate;
And baking the coating to form a piezoelectric / electrostrictive film made of tetragonal perovskite.   In the general formula, the A site further includes at least one A site substitution element selected from Bi, Ba, Sr, Ca, La, Ce, Nd, Sm, Dy, Ho, Yb, and Ag. The method described.   The method according to claim 2, wherein the A site substitution element accounts for 0.5 atomic% or less of all atoms constituting the A site.   The B site according to any one of claims 1 to 3, further comprising at least one B site substitution element selected from Ta, Sb, Ti, Zr, V, Cr, Fe, Co, Ni, and Cu in the general formula. The method according to one item.   The method according to claim 4, wherein the B site substitution element accounts for 50 atomic% or less of all atoms constituting the B site.   The method according to claim 1, wherein 1 ≦ x ≦ 1.05 in the general formula.   The method according to claim 1, wherein the piezoelectric / electrostrictive film further includes at least one selected from the group consisting of Mn and Zn.   In the calcination, the raw material powder is heated to a temperature of 900 to 1200 ° C. at a rate of temperature increase of 200 to 2000 ° C./h, held at the temperature for 0 to 10 minutes, and 200 to 2000 ° C. from the temperature to 800 ° C. The method according to claim 1, wherein the method is performed according to a temperature profile including cooling at a rate of temperature decrease of / h.   The method according to claim 8, wherein in the temperature profile, a temperature time area calculated by multiplying a temperature by time in a temperature region of 800 ° C. or higher is 67 to 200 ° C. · h.   The method as described in any one of Claims 1-9 which further includes the process of pre-calcining the said raw material powder at the temperature of 600-900 degreeC before the said calcination process, and obtaining a pre-calcination thing.   The method according to claim 10, further comprising a step of pulverizing the preliminary calcined product.   The method according to claim 1, wherein the calcination is performed at 900 to 1200 ° C. for 0 to 20 hours.   The method according to claim 1, wherein the coating is formed by a screen printing method.   The substrate includes an inorganic oxide base material and a lower electrode layer formed on the inorganic oxide base material, and the piezoelectric / electrostrictive film is formed on the lower electrode layer. The method according to claim 1.   The method according to claim 14, wherein the inorganic oxide base material comprises at least one selected from the group consisting of zirconium oxide, aluminum oxide, magnesium oxide, mullite, aluminum nitride, silicon nitride, and glass.   The method of claim 14, wherein the inorganic oxide substrate comprises zirconium oxide.   The lower electrode layer comprises at least one selected from the group consisting of at least one metal selected from platinum, palladium, rhodium, gold and silver, or an alloy of two or more metals selected from the group. The method according to any one of claims 14 to 16.   Forming the intermediate electrode layer on the coating containing the calcined / ground powder before the firing, and further forming the coating containing the calcined / ground powder on the intermediate electrode layer, The method according to any one of claims 1 to 17, which is performed once or a plurality of times.

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