JP4367949B2 - Piezoelectric element and manufacturing method thereof - Google Patents

Description

  The present invention relates to a piezoelectric ceramic composition suitable for use in piezoelectric layers of various piezoelectric elements such as actuators, piezoelectric buzzers, sounding bodies and sensors, and further relates to a piezoelectric element using the same.

  For example, an actuator that uses displacement generated by the piezoelectric effect as a mechanical drive source has advantages such as low power consumption and heat generation, good response, and miniaturization and weight reduction. However, it has come to be used in a wide range of fields.

Piezoelectric ceramic compositions used for this type of actuator are required to have a large piezoelectric characteristic, particularly a piezoelectric strain constant. Examples of piezoelectric ceramic compositions that satisfy this requirement include lead titanate (PbTiO ₃ ) and lead zirconate. (PbZrO ₃ ) and zinc / lead niobate [Pb (Zn _1/3 Nb _2/3 ) O ₃ ], a ternary piezoelectric ceramic composition, and the ternary piezoelectric ceramic composition Piezoelectric ceramic compositions in which a part of Pb, which is a constituent element, is substituted with Sr, Ba, Ca, or the like have been developed.

  However, these conventional piezoelectric ceramic compositions need to be fired at a relatively high temperature, and since firing is performed in an oxidizing atmosphere, for example, in a laminated actuator that simultaneously fires internal electrodes, a high melting point is obtained. It is necessary to use a noble metal (for example, Pt, Pd, etc.) that does not oxidize even when fired in an oxidizing atmosphere. As a result, the cost is increased and the cost of the manufactured piezoelectric element is hindered.

  From such a situation, the applicant of the present application includes, in the ternary piezoelectric ceramic composition, a first subcomponent including at least one selected from Fe, Co, Ni, and Cu, and Sb, Nb, and Ta. It has been proposed that low temperature firing is possible by adding a second subcomponent including at least one selected, and that an inexpensive material such as an Ag—Pd alloy can be used for the internal electrode (see Patent Document 1). ).

The invention described in Patent Document 1 includes the ternary piezoelectric ceramic composition and the piezoelectric ceramic composition in which part of Pb is replaced with Sr, Ba, Ca, etc. in the ternary piezoelectric ceramic composition. By adding a first subcomponent including at least one selected from Co, Ni, and Cu and a second subcomponent including at least one selected from Sb, Nb, and Ta, a high piezoelectric strain constant is obtained. Provided is a piezoelectric ceramic composition that is densified without impairing various piezoelectric characteristics even when fired at a low temperature and has increased mechanical strength, and has a piezoelectric layer composed of the piezoelectric ceramic composition. That's it.
JP 2004-137106 A

  However, when using a cheaper metal (Cu) as an electrode material, it is not sufficient to perform low-temperature baking only by adding the subcomponents. For example, in baking in an oxidizing atmosphere such as in air, There is a risk that the electrode material is oxidized and the conductivity is impaired.

In order to eliminate the above disadvantages, it is necessary to perform firing in a reducing atmosphere having a low oxygen partial pressure (the oxygen partial pressure is about 1 × 10 ⁻⁹ to 1 × 10 ⁻⁶ atm). However, when firing is performed in a reducing atmosphere, the obtained fired body contains more oxygen vacancies than a sintered body fired in air, and thus there is a high possibility that the insulation life will be reduced. Decreasing the insulation life impairs the reliability of the product, which is a big problem.

  The present invention has been proposed in view of such conventional circumstances, and an object of the present invention is to provide a highly reliable piezoelectric magnetic composition in which a decrease in insulation life is suppressed, and further provides a piezoelectric element. The purpose is to do.

  In order to achieve the above object, the present inventors have made various studies over a long period of time. As a result, for example, by making the annealing conditions after firing appropriate, oxygen vacancies contained in the sintered body of the piezoelectric ceramic composition can be suppressed, and the temperature change of the specific resistance value is included in the sintered body. As a result, it has been found that a piezoelectric ceramic composition having an excellent insulation life can be realized by defining this.

The present invention has been completed based on such findings. That is, the piezoelectric element of the present invention includes a plurality of piezoelectric layers formed of a piezoelectric ceramic composition, and an internal electrode layer formed so as to be inserted between the piezoelectric layers. Or containing Ni, the piezoelectric ceramic composition may be Pb _a [(Zn _1/3 Nb _2/3 ) _x Ti _y Zr _z ] O ₃ (provided that 0.96 ≦ a ≦ 1.03, 0.05 ≦ x ≦ 0.15, 0.25 ≦ y ≦ 0.5, 0.35 ≦ z ≦ 0.6, and x + y + z = 1.), And (Pb _a−b Me _b ) [(Zn _1/3 Nb _2/3 ) _x Ti _y Zr _z ] O ₃ (where 0.96 ≦ a ≦ 1.03, 0 <b ≦ 0.1, 0.05 ≦ x ≦ 0.15) 0.25 ≦ y ≦ 0.5, 0.35 ≦ z ≦ 0.6, x + y + z = 1, and Me in the formula is Sr, Ca, B At least one selected from the complex oxides represented by the formula (1), IR (150 ° C) as the specific resistance value at 150 ° C, and IR as the specific resistance value at 50 ° C. (50 ° C.), IR (150 ° C.) / IR (50 ° C.) ≧ 0.05. The method for manufacturing a piezoelectric element of the present invention includes a plurality of piezoelectric layers formed of a piezoelectric ceramic composition, and an internal electrode layer formed so as to be inserted between the piezoelectric layers. Contains Cu or Ni, and the piezoelectric ceramic composition is Pb _a [(Zn _1/3 Nb _2/3 ) _x Ti _y Zr _z ] O ₃ (where 0.96 ≦ a ≦ 1.03, 0.05 ≦ x ≦ 0.15, 0.25 ≦ y ≦ 0.5, 0.35 ≦ z ≦ 0.6, and x + y + z = 1.), And (Pb _{a− b} Me _b ) [(Zn _1/3 Nb _2/3 ) _x Ti _y Zr _z ] O ₃ (where 0.96 ≦ a ≦ 1.03, 0 <b ≦ 0.1, 0.05 ≦ x ≦ 0.15, 0.25 ≦ y ≦ 0.5, 0.35 ≦ z ≦ 0.6, and x + y + z = 1, and Me in the formula is Sr, C , Represents at least one selected from Ba.), And is a method of manufacturing a piezoelectric element including at least one selected from a composite oxide represented by: a ceramic precursor layer formed by a ceramic raw material mixture and an internal electrode An internal electrode precursor layer formed from a raw material mixture is laminated to form a laminated body, and the laminated body is subjected to reduction firing , and then annealed in an atmosphere having an oxygen partial pressure of 10 ⁻⁵ atm or more.

  As described above, the piezoelectric ceramic composition of the present invention is such that the ratio between the specific resistance value at 150 ° C. and the specific resistance value at 50 ° C. is not less than a predetermined value. Mean small. The temperature change of the specific resistance value becomes an index of the amount of oxygen vacancies contained in the piezoelectric ceramic composition, and if the temperature change is small, the amount of oxygen vacancies is small and the insulation life is less decreased.

  According to the present invention, as described above, it is possible to provide a piezoelectric ceramic composition having few oxygen vacancies by defining the ratio between the specific resistance value at 150 ° C. and the specific resistance value at 50 ° C. . Therefore, it is possible to provide a piezoelectric ceramic composition and a piezoelectric element that have excellent insulation life and high reliability.

  Hereinafter, a piezoelectric ceramic composition and a piezoelectric element to which the present invention is applied will be described in detail with reference to the drawings.

First, the piezoelectric ceramic composition of the present invention is mainly composed of a complex oxide containing Pb, Ti, and Zr as constituent elements. Here, the composite oxide is composed of, for example, lead titanate (PbTiO ₃ ), lead zirconate (PbZrO ₃ ), and zinc / lead niobate [Pb (Zn _1/3 Nb _2/3 ) O ₃ ]. Or a composite oxide obtained by substituting a part of Pb with Sr, Ba, Ca, or the like in the ternary composite oxide.

  Specific examples of the composition include composite oxides represented by the following formula (1) or (2). In these formulas (1) and (2), the oxygen composition is obtained stoichiometrically, and deviation from the stoichiometric composition is allowed in the actual composition. .

Pb _a [(Zn _1/3 Nb _2/3 ) _x Ti _y Zr _z ] O ₃ (1)
(However, 0.96 ≦ a ≦ 1.03, 0.05 ≦ x ≦ 0.15, 0.25 ≦ y ≦ 0.5, 0.35 ≦ z ≦ 0.6, and x + y + z = 1.)

(Pb _a-b Me _b ) [(Zn _1/3 Nb _2/3 ) _x Ti _y Zr _z ] O ₃ (2)
(However, 0.96 ≦ a ≦ 1.03, 0 <b ≦ 0.1, 0.05 ≦ x ≦ 0.15, 0.25 ≦ y ≦ 0.5, 0.35 ≦ z ≦ 0.6 X + y + z = 1, and Me in the formula represents at least one selected from Sr, Ca, and Ba.)

  The composite oxide has a so-called perovskite structure, and Pb and the substitution element Me in the formula (2) are located at a so-called A site of the perovskite structure. Zn, Nb, Ti, and Zr are located at the so-called B site of the perovskite structure.

  In the composite oxide represented by the formula (1) or formula (2), the ratio a of the A site element is preferably 0.96 ≦ a ≦ 1.03. If the A-site element ratio a is less than 0.96, firing at low temperatures may be difficult. On the contrary, when the ratio a of the A site element exceeds 1.03, the density of the obtained piezoelectric ceramic is lowered, and as a result, sufficient piezoelectric characteristics may not be obtained, and the mechanical strength may also be lowered. is there.

  In the composite oxide represented by the above formula (2), a part of Pb is substituted with the substitution element Me (Sr, Ca, Ba), but this can increase the piezoelectric strain constant. However, if the substitution amount b of the substitution element Me is too large, the sinterability is lowered, and as a result, the piezoelectric strain constant is reduced and the mechanical strength is also lowered. Also, the Curie temperature tends to decrease as the substitution amount b increases. Therefore, the substitution amount b of the substitution element Me is preferably 0.1 or less.

  On the other hand, among the B site elements, the ratio x between Zn and Nb is preferably 0.05 ≦ x ≦ 0.15. The ratio x affects the firing temperature. If this value is less than 0.05, the effect of lowering the firing temperature may be insufficient. On the other hand, if it exceeds 0.15, the sinterability is affected, and as a result, the piezoelectric strain constant may be reduced and the mechanical strength may be reduced.

  Of the B-site elements, the Ti ratio y and the Zr ratio z are preferably set in terms of piezoelectric characteristics. Specifically, the Ti ratio y is preferably 0.25 ≦ y ≦ 0.5, and the Zr ratio z is preferably 0.35 ≦ z ≦ 0.6. By setting it within the above range, a large piezoelectric strain constant can be obtained in the vicinity of the morphotropic phase boundary (MPB).

The piezoelectric ceramic composition of the present invention contains the composite oxide as a main component, but may contain subcomponents in addition to this. In this case, the subcomponent is at least one selected from Ta, Sb, Nb, and W. By adding the subcomponent, piezoelectric characteristics and mechanical strength can be improved. However, the content of these subcomponents is preferably 1.0% by mass or less in terms of oxide. For example, in the case of Ta, 1.0% by mass or less in terms of Ta ₂ O ₅ , in the case of Sb, 1.0% by mass or less in terms of Sb ₂ O ₃ , and in the case of Nb, 1.0% by mass in terms of Nb ₂ O ₅ Hereinafter, in the case of W, it is 1.0 mass% or less in terms of WO ₃ . If the content of the subcomponent exceeds 1.0% by mass in terms of the oxide, the sinterability may be reduced and the piezoelectric characteristics may be deteriorated.

  As described above, the piezoelectric ceramic composition of the present invention is mainly composed of a composite oxide containing Pb, Ti, and Zr as constituent elements, but the temperature change (degree of decrease due to temperature) of the specific resistance value is large. It is small. Specifically, when the specific resistance value at 150 ° C. is IR (150 ° C.) and the specific resistance value at 50 ° C. is IR (50 ° C.), IR (150 ° C.) / IR (50 ° C.) ≧ 0 .05.

  The specific resistance value of the piezoelectric ceramic composition decreases with an increase in temperature. However, in the above definition, the larger the value, the smaller the decrease in specific resistance value with increasing temperature. Ideally, IR (150 ° C.) / IR (50 ° C.) = 1, but it is actually difficult, and in the present invention, it is 0.05 or more as described above. More preferably, IR (150 ° C.) / IR (50 ° C.) ≧ 0.1.

  The value of IR (150 ° C.) / IR (50 ° C.) is an index of oxygen vacancies contained in the sintered body of the piezoelectric ceramic composition. According to the above definition, the sintered body of the piezoelectric ceramic composition The amount of oxygen vacancies contained in is defined. Then, by setting the IR (150 ° C.) / IR (50 ° C.) to 0.05 or more, a piezoelectric ceramic composition having a long insulation life can be provided even when firing is performed in a reducing atmosphere, for example. It becomes possible.

  The piezoelectric ceramic composition described above can be used for, for example, a laminated piezoelectric element formed by inserting an internal electrode layer between a plurality of piezoelectric layers. Hereinafter, a piezoelectric element using the piezoelectric ceramic composition of the present invention will be described.

  FIG. 1 shows an example of a laminated piezoelectric element. As shown in FIG. 1, the multilayer piezoelectric element 1 includes a multilayer body 4 in which an internal electrode layer 3 is inserted between a plurality of piezoelectric layers 2, and the multilayer body 4 is displaced as an active portion. Contribute. Although the thickness per layer of the piezoelectric layer 2 can be set arbitrarily, it is usually set to about 1 μm to 100 μm, for example. On both sides of the multilayer body 4, there are piezoelectric layer regions in which the internal electrode layer 3 is not formed as inactive regions. The thickness of the piezoelectric layer in this portion is the thickness of the piezoelectric layer 2 between the internal electrode layers 3. In some cases, the thickness is set to be thicker.

  The internal electrode layers 3 are alternately extended in opposite directions, for example, and terminal electrodes 5 and 6 electrically connected to the internal electrode layers 3 are provided at end portions in the extension directions. The terminal electrodes 5 and 6 may be formed, for example, by sputtering a metal such as Au, or may be formed by baking an electrode paste. The thicknesses of the terminal electrodes 5 and 6 are appropriately set depending on the application, the size of the multilayer piezoelectric element 1 and the like, but are usually about 10 μm to 50 μm.

  In the piezoelectric element, the internal electrode layer 3 has a function as an electrode for applying a voltage to each piezoelectric layer 2 and is naturally formed of a conductive material. In this case, a noble metal such as Ag, Au, Pt, or Pd can be used as the conductive material, but it is preferable to use an electrode material containing Cu or Ni in view of manufacturing cost. Specifically, the internal electrode layer 3 is formed by applying a Cu paste or the like. By using the base metal such as Cu as an electrode material, the manufacturing cost of the multilayer piezoelectric element 1 can be reduced.

  On the other hand, a piezoelectric ceramic composition is used for the piezoelectric layer 2. The piezoelectric ceramic composition to be used is a piezoelectric ceramic mainly composed of a composite oxide containing Pb, Ti, and Zr as described above. It is a composition. In this piezoelectric ceramic composition, when the specific resistance value at 150 ° C. is IR (150 ° C.) and the specific resistance value at 50 ° C. is IR (50 ° C.), IR (150 ° C.) / IR ( 50 ° C.) ≧ 0.05.

In the above-described piezoelectric element, in consideration of using a base metal such as Cu for the internal electrode layer 3, it is preferably fired under reducing firing conditions. When the piezoelectric element is manufactured, if it is fired in an oxidizing atmosphere, it is necessary to use a noble metal as the electrode material of the internal electrode layer 3. On the other hand, if firing is performed under reducing firing conditions, inexpensive Cu or the like can be used for the internal electrode layer 3. Here, the reduction firing conditions are, for example, a firing temperature of 800 ° C. to 1200 ° C. and an oxygen partial pressure of 1 × 10 ⁻¹⁰ to 1 × 10 ⁻⁶ atm.

  However, when firing is performed under the above-described reducing firing conditions, a decrease in insulation life due to an increase in oxygen vacancies becomes a problem. Therefore, when the piezoelectric element is manufactured, for example, annealing is performed in an atmosphere having a predetermined oxygen partial pressure after the reduction firing, thereby suppressing the oxygen vacancies, and IR (150 ° C.) / IR (50 ° C.) is 0. Try to be over 05. Hereinafter, an example of a manufacturing method suitable for manufacturing the piezoelectric element 1 of the present invention will be described.

In order to manufacture the piezoelectric element 1, first, a ceramic precursor layer forming step, an internal electrode raw material mixture forming step, and a laminating step for laminating them are performed. In the ceramic precursor layer forming step, the piezoelectric layer 2 raw materials are prepared and weighed according to the target composition, and then a binder or the like is added to obtain a ceramic raw material mixture. The raw material of the piezoelectric layer 2 includes oxides, carbonates, oxalates, hydroxides, etc. of the elements constituting the piezoelectric layer 2. For example, the piezoelectric layer 2 is made of the above lead zirconate titanate. In some cases, lead oxide (PbO), titanium oxide (TiO ₂ ), and zirconium oxide (ZrO ₂ ) are used as raw materials. Next, the ceramic raw material mixture is formed into a sheet shape to form a ceramic precursor layer.

  Similarly, in the formation process of the internal electrode raw material mixture, for example, metallic copper as a raw material of the internal electrode layer 3 is prepared, and a binder or the like is added to obtain an internal electrode raw material mixture. As a raw material for the internal electrode layer 3, the metal copper may be used alone or in combination with other materials. In this case, examples of the other material include a copper oxide or an organic copper compound that becomes metal copper after firing, a metal other than metal copper, a metal oxide, an organic metal compound, and the like. Moreover, you may add additives, such as a dispersing agent, a plasticizer, a dielectric material, an insulator material, to an internal electrode raw material mixture as needed.

  In the laminating step, the internal electrode precursor layer is formed by, for example, screen printing the internal electrode raw material mixture on the ceramic precursor layer. As described above, a plurality of ceramic precursor layers on which the internal electrode precursor layers are formed are stacked to obtain a stacked body in which the ceramic precursor layers and the internal electrode precursor layers are alternately stacked. The method of forming the laminate is not limited to this, and the laminate may be formed by alternately printing the ceramic raw material mixture and the internal electrode raw material mixture, or the ceramic raw material mixture and the internal electrode raw material mixture may be formed into sheets, respectively. Then, it may be formed by stacking.

  After the above-described lamination process, the binder removal process is performed on the obtained laminate in the binder removal process. The binder removal step is a step of decomposing and removing the ceramic precursor layers and the binder contained in the internal electrode precursor layers constituting the laminate by heating.

Also in this binder removal treatment, it is necessary to consider the oxidation of the conductive material in the internal electrode precursor layer, and it is preferable to employ heating in a reducing atmosphere. On the other hand, it is necessary to consider that the oxide, for example, PbO, contained in the piezoelectric ceramic layer precursor is reduced in the binder removal treatment. This is because, depending on the degree of reduction, a sufficient amount of oxygen may not be supplied by the oxygen supply heating described later. Therefore, for example, when Cu is used as the internal electrode material, the equilibrium oxygen partial pressure of Cu and Cu ₂ O (hereinafter simply referred to as the equilibrium oxygen partial pressure of Cu) and the equilibrium oxygen partial pressure of Pb and PbO (hereinafter simply referred to as “equal oxygen partial pressure”). It is preferable to appropriately set the atmosphere for the binder removal processing based on the equilibrium oxygen partial pressure of Pb.

  FIG. 2 shows the equilibrium oxygen partial pressure of Cu and the equilibrium oxygen partial pressure of Pb. Theoretically, the oxygen partial pressure in a region surrounded by two curves indicating the equilibrium oxygen partial pressure is shown in FIG. When the binder removal process is performed, Pb is not reduced and Cu is not oxidized. Since the binder removal treatment is preferably performed in a temperature range of 300 ° C. to 650 ° C., the atmosphere of the binder removal treatment is an oxygen partial pressure in the vicinity of the hatched region in the drawing or in the vicinity thereof. It is preferable.

  As described above, the binder removal treatment is preferably performed in a temperature range of 300 ° C. to 650 ° C. If the temperature of the binder removal treatment is less than 300 ° C., the binder removal cannot be performed smoothly. Conversely, even if the temperature of the binder removal process exceeds 650 ° C., a binder removal effect corresponding to the temperature cannot be obtained, leading to wasted energy. The binder removal time needs to be determined depending on the temperature and atmosphere, but can be selected in the range of 0.5 to 50 hours. Furthermore, the binder removal treatment may be performed independently of the firing, or may be performed continuously with the firing. In the latter case, the binder removal process may be performed during the heating process.

After the binder removal treatment, firing is performed, but the firing is performed in a reducing atmosphere. This is for preventing or suppressing oxidation of a base metal such as Cu used for the internal electrode layer. The specific reducing atmosphere to be used needs to take into account the equilibrium oxygen partial pressure of Cu and the equilibrium oxygen partial pressure of Pb, as in the case of the binder removal treatment. Since the firing is performed at a higher temperature than the binder removal treatment, as is apparent from FIG. 2, the firing is performed in an atmosphere having a higher oxygen partial pressure than the reducing atmosphere during the binder removal treatment. For example, since it is recommended that the firing be performed in a temperature range of 800 ° C. to 1200 ° C., the firing atmosphere is set to an oxygen partial pressure in the vicinity of the hatched region in FIG. 2 or in the vicinity thereof. A reducing atmosphere is preferable. Specifically, the oxygen partial pressure is preferably 10 ⁻⁶ to 10 ⁻¹⁰ atm. When the firing temperature is less than 800 ° C., a dense sintered body cannot be obtained, and when it exceeds 1080 ° C., the electrode material constituting the internal electrode may be melted.

  Next, oxygen supply heat treatment (so-called annealing treatment) is performed. This heat treatment is performed in a predetermined oxygen partial pressure atmosphere for the purpose of preventing a decrease in insulation life. By firing in the reducing atmosphere, lattice defects are generated in the crystal grains of the piezoelectric ceramic layer, and oxygen vacancies are increased. By the annealing treatment in the predetermined oxygen partial pressure atmosphere, oxygen is supplemented, and oxygen vacancies are reduced.

In the case of manufacturing a laminated piezoelectric element in which an internal electrode is made of a base metal, the annealing atmosphere is preferably an oxygen partial pressure of 10 ⁻⁵ atm or more, and more preferably an oxygen partial pressure of 10 ⁻³ atm or more. preferable. In the annealing treatment, if the heat treatment atmosphere contains excessive oxygen, the internal electrode layer composed of the base metal is oxidized, so that the contained oxygen must be regulated. Therefore, the oxygen partial pressure is preferably less than 10 ⁻¹ atm.

  In the annealing process, if the heat treatment temperature is low, it becomes difficult to supply oxygen to the crystal grain boundaries or grains in the piezoelectric ceramic layer. Conversely, if the heat treatment temperature is too high, the internal electrode layer made of a base metal may be oxidized. Considering these, the annealing temperature is preferably set to 600 ° C. or higher. However, it is not preferable that the heat treatment temperature exceeds 900 ° C., because firing proceeds instead of annealing. Note that the temperature in the annealing process may be constant or varied within the above range. The annealing temperature is set to a temperature lower than the preceding firing temperature.

  The annealing time needs to be varied depending on the annealing atmosphere (oxygen partial pressure) and temperature, but if it is too short, oxygen cannot be supplied sufficiently. Moreover, even if it takes longer time than necessary, the effect is saturated and energy is wasted. Therefore, the annealing time is preferably 2 to 8 hours.

  The annealing treatment described above can be performed as an independent process separate from the firing process, or can be performed continuously with the firing. FIG. 3 shows a temperature profile when the annealing treatment is performed independently of the firing step. As shown in FIG. 3, the firing step includes a temperature raising process, a holding process, and a temperature lowering process. When the annealing process is performed independently of the firing process, the temperature is raised to the annealing temperature after the temperature lowering process of the firing process is completed, and the temperature is lowered after being held for a predetermined time. Such an embodiment can be applied, for example, when firing and annealing are performed using different heating furnaces.

  On the other hand, when the annealing treatment is performed continuously with the firing, as shown in FIG. That is, as shown in FIG. 4, the annealing process can be performed by holding for a predetermined time in the annealing temperature range in the temperature lowering process of firing. After the annealing treatment temperature is maintained for a predetermined time, the temperature may be lowered in the same manner as the temperature lowering process of firing. Since the atmospheres of the firing and the annealing treatment are different as described above, it is necessary to change the firing atmosphere to the annealing treatment atmosphere at least before reaching the annealing treatment temperature. Such an embodiment can be applied, for example, when firing and annealing are performed using the same heating furnace.

  The laminated piezoelectric element manufactured through the above steps is subjected to end face polishing, for example, by barrel polishing or sandblasting, and a terminal electrode is formed by printing or baking terminal electrode paste. Note that the method for forming the terminal electrode is not limited to this, and it is also possible to form the terminal electrode by sputtering the electrode material and then patterning it in addition to the printing and baking.

  Hereinafter, specific examples to which the present invention is applied will be described based on experimental results.

Experiment 1: Examination of oxygen partial pressure during annealing treatment A piezoelectric ceramic composition was prepared as follows. First, PbO powder, SrCO ₃ powder, ZnO powder, Nb ₂ O ₅ powder, TiO ₂ powder, and ZrO ₂ powder were prepared as raw materials of the main component, and weighed so as to have the following main component composition. Next, these raw materials were wet-mixed for 16 hours using a ball mill, and calcined at 700 ° C. to 900 ° C. for 2 hours in the air.
Main component: (Pb _0.965 Sr _0.03 ) [(Zn _1/3 Nb _2/3 ) _0.1 Ti _0.43 Zr _0.47 ] O ₃

The obtained calcined product was finely pulverized and then wet pulverized for 16 hours using a ball mill. After drying this, an acrylic resin was added as a binder for granulation, and it was formed into a disk shape having a diameter of 17 mm and a thickness of 1 mm using a uniaxial press molding machine at a pressure of about 445 MPa. After molding, a Cu paste containing Cu powder having a particle size of 1.0 μm was printed on both sides. The obtained pellets were heat-treated to volatilize the binder and fired at 950 ° C. for 8 hours in a low oxygen reducing atmosphere (oxygen partial pressure 1 × 10 ⁻¹⁰ to 1 × 10 ⁻⁶ atm). After firing, annealing was performed at 700 ° C. for 2 hours in an atmosphere having an oxygen partial pressure of 10 ⁻⁷ atm to 10 ⁻¹ atm.

  The obtained sintered body was formed into a disk shape having a thickness of 0.6 mm by slicing and lapping, and the printed Cu paste was removed, and at the same time processed into a shape capable of evaluating the characteristics. A silver paste was printed on both surfaces of the obtained sample and baked at 350 ° C., and an electric field of 3 kV was applied in 120 ° C. silicone oil for 15 minutes to carry out polarization treatment.

  Under each annealing treatment condition, five samples were prepared, and the specific resistance at 150 ° C. and 50 ° C. was measured to calculate the value of IR (150 ° C.) / IR (50 ° C.). Moreover, while performing the high temperature load life test about each sample, the high temperature load life improvement degree was evaluated. In the high-temperature load life test, a voltage of 3.2 kV was applied to five samples so that the electric field strength was 8 kV / mm at a temperature of 250 ° C., and the change over time in the insulation resistance was obtained. Here, the time until the insulation resistance of each sample decreased by one digit or more on the basis of the value immediately after the start of the test was measured as the life time, and was defined as the high temperature load life. The high temperature load life improvement degree is x when the life time is zero, ○ when the sample does not crack until the insulation resistance decreases by one digit, and when the sample cracks before the insulation resistance decreases by one digit Was represented by Δ. The results are shown in Table 1. In addition, FIG. 5 shows how the specific resistance of each sample changes with temperature.

First, as is clear from FIG. 1, the temperature change of the specific resistance is reduced by increasing the oxygen partial pressure during the annealing treatment, and the oxygen partial pressure is set to 1 × 10 ⁻⁵ atm or more at 150 ° C. The value of the specific resistance exceeds 1 × 10 ¹² Ω · cm. Moreover, as apparent from Table 1, the high temperature load life is improved with the increase of the oxygen partial pressure, and particularly at an oxygen partial pressure of 1 × 10 ⁻³ atm or more, cracks do not occur in all samples. As a result, the improvement degree of the high temperature load life is high. The oxygen partial pressure of 1 × 10 ⁻⁵ atm or more corresponds to IR (150 ° C.) / IR (50 ° C.) ≧ 0.05, and the oxygen partial pressure of 1 × 10 ⁻³ atm or more corresponds to IR (150 ° C. ) / IR (50 ° C.) ≧ 0.1.

Experiment 2: Examination of annealing temperature A sample of a piezoelectric ceramic composition was prepared in the same manner as in Experiment 1 except that the annealing temperature was changed from 500 ° C to 800 ° C. The oxygen partial pressure in the annealing treatment was 1 × 10 ⁻⁵ atm, and the treatment time was 2 hours. For these samples, the specific resistance at 150 ° C. and 50 ° C. was measured to calculate the value of IR (150 ° C.) / IR (50 ° C.), a high temperature load life test was conducted, and the improvement degree of the high temperature load life was evaluated. The results are shown in Table 2. Further, FIG. 6 shows a difference in temperature change of specific resistance due to a difference in annealing temperature.

  As is apparent from Table 2 and FIG. 6, by setting the annealing temperature to 600 ° C. or higher, IR (150 ° C.) / IR (50 ° C.) ≧ 0.05, and the effect of improving the insulation life is seen. It is done.

Experiment 3: Examination of annealing time A sample of a piezoelectric ceramic composition was prepared in the same manner as in Experiment 1 except that the annealing time was changed from 2 hours to 8 hours. The oxygen partial pressure in the annealing treatment was 1 × 10 ⁻⁵ atm, and the annealing treatment temperature was 700 ° C. For these samples, the specific resistance at 150 ° C. and 50 ° C. was measured to calculate the value of IR (150 ° C.) / IR (50 ° C.), a high temperature load life test was conducted, and the improvement degree of the high temperature load life was evaluated. The results are shown in Table 3. Further, FIG. 7 shows a difference in temperature change of specific resistance due to a difference in annealing treatment time.

  As is apparent from Table 3 and FIG. 7, by setting the annealing time to 2 hours or longer, IR (150 ° C.) / IR (50 ° C.) ≧ 0.05, and the effect of improving the insulation life is seen. It is done.

Experiment 4: Change in oxygen vacancy amount due to annealing treatment CL (cathode luminescence) spectrum of a piezoelectric ceramic composition that had been subjected to annealing treatment at 700 ° C. for 2 hours in an atmosphere having an oxygen partial pressure of 10 ⁻⁵ atm after reduction firing. Was measured. Cathodoluminescence is the light generated in the process where electrons in the valence band of crystals are excited and recombined when irradiated with electrons accelerated at high speed. It is used as a technique for observing defects.

  In the analysis, the fired sample was embedded in a resin, polished, and mirror-finished with a 1.0 μm diamond paste, and then carbon deposition was performed. And the cathode luminescence was measured about this carbon vapor deposition surface. As a measuring apparatus, a cathode luminescence detection apparatus attached to an X-ray microanalyzer EMX-SM type manufactured by Shimadzu Corporation was used. The measurement conditions of the CL spectrum are an acceleration voltage of 25 keV, an irradiation current of 200 mA, a wavelength scanning speed of 2000 km / min, a beam diameter of 200 μm, and an integration time of 2000 msec. The results are shown in FIG. FIG. 8 also shows the measurement results of a sample fired in air and a sample fired by reduction firing (without annealing treatment).

  As can be seen from FIG. 8, the annealed piezoelectric ceramic composition has a lower CL peak intensity than the piezoelectric ceramic composition simply reduced and fired. The CL peak intensity is presumed to be proportional to the amount of oxygen vacancies, and the oxygen vacancies are presumed to be reduced by the annealing treatment.

It is a schematic sectional drawing which shows one structural example of a lamination type piezoelectric element. It is a characteristic figure which shows the equilibrium oxygen partial pressure curve of Cu, and the equilibrium oxygen partial pressure curve of Pb. It is a figure which shows an example of the temperature profile in the case of performing an annealing process separately from baking. It is a figure which shows an example of the temperature profile in the case of performing an annealing process in the temperature-fall process after baking. It is a characteristic view which shows the difference in the temperature change of the specific resistance by the oxygen partial pressure at the time of annealing treatment. It is a characteristic view which shows the difference in the temperature change of the specific resistance by annealing process temperature. It is a characteristic view which shows the difference in the temperature change of the specific resistance by annealing treatment time. It is a characteristic view which shows the measurement result of CL spectrum.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric element, 2 Piezoelectric layer, 3 Internal electrode, 4 Laminated body, 5, 6 Terminal electrode

Claims (6)

A plurality of piezoelectric layers formed of the piezoelectric ceramic composition, and an internal electrode layer formed in a form to be inserted between the piezoelectric layers,
The internal electrode layer contains Cu or Ni,
The piezoelectric ceramic composition is Pb. _a [(Zn _1/3 Nb _2/3 ) _x Ti _y Zr _z ] O ₃ (However, 0.96 ≦ a ≦ 1.03, 0.05 ≦ x ≦ 0.15, 0.25 ≦ y ≦ 0.5, 0.35 ≦ z ≦ 0.6, and x + y + z = 1.) And (Pb _a-b Me _b ) [(Zn _1/3 Nb _2/3 ) _x Ti _y Zr _z ] O ₃ (However, 0.96 ≦ a ≦ 1.03, 0 <b ≦ 0.1, 0.05 ≦ x ≦ 0.15, 0.25 ≦ y ≦ 0.5, 0.35 ≦ z ≦ 0.6 X + y + z = 1 In addition, Me in the formula represents at least one selected from Sr, Ca, and Ba.) And includes at least one selected from complex oxides represented by 150 ° C. IR (150 ° C.) / IR (50 ° C.) ≧ 0.05 when the specific resistance value of IR is 150 ° C. and the specific resistance value at 50 ° C. is IR (50 ° C.) Piezoelectric element. The piezoelectric element according to claim 1, wherein IR (150 ° C.) / IR (50 ° C.) ≧ 0.1. The piezoelectric ceramic composition contains at least one selected from Ta, Sb, Nb and W as subcomponents, and the content of the subcomponents is 1.0% by mass or less in terms of oxide. The piezoelectric element according to claim 1 or 2. A plurality of piezoelectric layers formed of a piezoelectric ceramic composition; and an internal electrode layer formed so as to be inserted between the piezoelectric layers, the internal electrode layer containing Cu or Ni, and the piezoelectric ceramic The composition is Pb _a [(Zn _1/3 Nb _2/3 ) _x Ti _y Zr _z ] O ₃ (However, 0.96 ≦ a ≦ 1.03, 0.05 ≦ x ≦ 0.15, 0.25 ≦ y ≦ 0.5, 0.35 ≦ z ≦ 0.6, and x + y + z = 1.) And (Pb _a-b Me _b ) [(Zn _1/3 Nb _2/3 ) _x Ti _y Zr _z ] O ₃ (However, 0.96 ≦ a ≦ 1.03, 0 <b ≦ 0.1, 0.05 ≦ x ≦ 0.15, 0.25 ≦ y ≦ 0.5, 0.35 ≦ z ≦ 0.6 X + y + z = 1 In addition, Me in the formula represents at least one selected from Sr, Ca, and Ba.) A method for manufacturing a piezoelectric element including at least one selected from complex oxides Because
Laminating a ceramic precursor layer formed of a ceramic raw material mixture and an internal electrode precursor layer formed of an internal electrode raw material mixture,
After reducing and firing the laminate, the oxygen partial pressure is 10 ^-5 A method of manufacturing a piezoelectric element, comprising annealing in an atmosphere of atm or higher. The reduction firing conditions are firing temperature 800 ° C. to 1200 ° C., oxygen partial pressure 1 × 10 ^-10 ~ 1x10 ^-6 The method of manufacturing a piezoelectric element according to claim 4, wherein the piezoelectric element is atm. 5. The method of manufacturing a piezoelectric element according to claim 4, wherein an annealing temperature in the annealing treatment is 600 ° C. or more and an annealing time is 2 hours or more.

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