JP4993056B2 - Manufacturing method and oxygen supply method of multilayer piezoelectric element - Google Patents

Description

  The present invention relates to a method for manufacturing a multilayer piezoelectric element formed by stacking a plurality of piezoelectric ceramic layers and a plurality of internal electrode layers.

  2. Description of the Related Art Conventionally, piezoelectric elements have been used as driving sources for various devices by utilizing the characteristic that electrical energy can be converted into mechanical energy by the piezoelectric effect. A general piezoelectric element has a structure in which a conductive paste is printed and fired on both sides of a piezoelectric ceramic layer such as lead zirconate titanate (PZT) to form an electrode layer. However, since the amount of displacement obtained with a single piezoelectric ceramic layer is small, when a relatively large amount of displacement is desired, the amount of displacement is increased by stacking the piezoelectric ceramic layers. The firing temperature of lead zirconate titanate or the like for obtaining this piezoelectric ceramic layer is as high as 1100 to 1200 ° C. Therefore, the material constituting the electrode layer must be able to withstand this high firing temperature. Therefore, noble metal particles such as Ag / Pt and Ag / Pd have been used as the conductive material used for the electrode layer so far, which has been a factor in increasing the manufacturing cost.

  However, in recent years, the piezoelectric ceramic material has been fired at a low temperature, and accordingly, a base metal material such as Cu can be used as the conductive material of the electrode layer, and the manufacturing cost can be reduced (for example, Special Table 2003). -529917 (patent document 1)).

Special table 2003-529917 gazette

A base metal material such as Cu is oxidized when fired in the air, and does not function as an electrode. Therefore, when an electrode layer is formed using a base metal material such as Cu, firing in a reducing atmosphere is required. For example, Patent Document 1 proposes using an atmosphere containing nitrogen, hydrogen, and water vapor to form a firing atmosphere in which Cu is not oxidized in consideration of the equilibrium partial pressure of Cu and Cu ₂ O.
However, by firing in a reducing atmosphere that does not oxidize Cu, the insulation resistance of the piezoelectric ceramic layer decreases when it reaches a high temperature of about 150 ° C., which may be a practical impediment to the multilayer piezoelectric element.
The present invention has been made on the basis of such a technical problem, and a reduction in insulation resistance at a high temperature occurring in a multilayer piezoelectric element fired in a reducing atmosphere using a base metal material such as Cu for an electrode layer. It is an object of the present invention to provide a multilayered piezoelectric element with improved characteristics.

  The present inventors performed heat treatment in an atmosphere having a predetermined oxygen partial pressure after firing. When the laminated piezoelectric element has an internal electrode made of Cu, this heat treatment should not oxidize the internal electrode made of Cu, but it is possible to insulate at a high temperature by adjusting the oxygen partial pressure and the heating temperature. It was confirmed that the decrease in resistance could be prevented.

The present invention based on the above is a method for manufacturing a laminated piezoelectric element in which a piezoelectric ceramic layer and an internal electrode are laminated, and includes a piezoelectric ceramic layer precursor containing a ceramic composition powder having a predetermined composition and a base metal as a conductive material. A firing step of firing the laminated body in which the internal electrode precursor is laminated in a first reducing atmosphere, and a second reduction in which the fired laminated body has a higher oxygen partial pressure than the first reducing atmosphere. A heat treatment step of heating in a neutral atmosphere, wherein the piezoelectric ceramic layer is made of a Pb-based piezoelectric material, and the first reducing atmosphere has an oxygen partial pressure of 10 ⁻⁶ to 10 ⁻⁹ atm and a second reducing atmosphere. The oxygen partial pressure is 10 ⁻² to 10 ⁻⁶ atm, the heating temperature T1 in the firing step is 800 to 1080 ° C., and the heating temperature T2 in the heat treatment step is 550 to 950 ° C. (where T1> T2). That features It is said.
In the heat treatment step, the second reducing atmosphere preferably has an oxygen partial pressure of 10 ⁻³ to 10 ⁻⁵ atm and a heating temperature T2 of 700 to 850 ° C. for the present invention.

According to the present invention, the conductivity can be substantially maintained without oxidizing the conductive material from the firing step to the heat treatment step. Further, by supplying oxygen into the piezoelectric ceramic layer in the heat treatment step, it is possible to suppress or prevent a decrease in insulation resistance at a high temperature.

  As described above, according to the present invention, when a laminated piezoelectric element having an internal electrode as a base metal such as Cu is manufactured by performing heat treatment in an atmosphere containing predetermined oxygen to supply oxygen, A reduction in insulation resistance in a high temperature range of about 150 ° C. can be prevented without oxidation.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
FIG. 1 is a cross-sectional view showing a configuration example of a multilayer piezoelectric element 1 obtained by the present invention. Note that FIG. 1 is merely an example, and it goes without saying that the present invention is not limited to the multilayer piezoelectric element 1 of FIG. The multilayer piezoelectric element 1 includes a multilayer body 10 in which a plurality of piezoelectric ceramic layers 11 and a plurality of internal electrodes 12 are alternately stacked. The thickness per layer of the piezoelectric ceramic layer 11 is preferably about 1 to 100 μm, for example, but the thickness of the piezoelectric ceramic layers 11 (11a, 11c) at the upper and lower ends is thicker than the piezoelectric ceramic layer 11 sandwiched between the internal electrodes 12. May form. Further, the number of stacked piezoelectric ceramic layers 11 is determined according to a target displacement amount.

The piezoelectric ceramic constituting the piezoelectric ceramic layer 11 is not particularly limited as long as it is made of a Pb-based piezoelectric material . However, since the present invention is premised on firing at a low temperature of, for example, 1050 ° C. or lower, it is desirable that the piezoelectric ceramic can be fired at such a low temperature. In the present invention, piezoelectric ceramics that can be fired at a low temperature can be widely used, but Pb-based piezoelectric ceramics containing a composition represented by the following composition formula are preferably used.
(Pb _1-B Me _B ) _A [(Zn _1/3 Nb _2/3 ) _a Ti _b Zr _c ] O ₃ , wherein the symbols Me, A, B, a, b and c in the formula are Me: at least one selected from Ca, Sr and Ba, 0.99 ≦ A ≦ 1.005, 0 ≦ B ≦ 0.1, 0.05 ≦ a ≦ 0.25, 0.35 ≦ b ≦ 0. A main component including an oxide having a composition of 50, 0.38 ≦ c ≦ 0.48, and a + b + c = 1, a first subcomponent including at least one selected from Fe, Co, Ni, and Cu, and Sb Any one or both of a second subcomponent containing at least one selected from Nb and Ta, wherein the ratio of each subcomponent to the mass of 1 mol of the main component is first subcomponent: oxides _{(NiO, CoO, Fe 2 O} 3, CuO) in terms of 0.01-0.8 wt%, Preliminary second subcomponent: oxide _{(Sb 2 O 3, Nb 2} O 5, Ta 2 O 5) to a piezoelectric ceramic which is 0.1 to 1 wt% as calculated.

The internal electrode 12 contains a conductive material. In the present invention, Cu can be used as the conductive material. Since the multilayer piezoelectric element 1 according to the present invention is premised on main firing at a low temperature of, for example, 1080 ° C. or lower, these low melting point conductive materials can be used.

For example, the internal electrodes 12 are alternately extended in opposite directions, and a pair of terminal electrodes 21 and 22 electrically connected to the internal electrode 12 are provided in the extending direction. The terminal electrodes 21 and 22 are electrically connected to an external power source (not shown) via a lead wire (not shown), for example.
Moreover, the terminal electrodes 21 and 22 may be formed by sputtering metals, such as Au, Ag, and Cu, for example, and may be formed by baking the paste for terminal electrodes. The terminal electrode paste contains, for example, a conductive material, glass frit, and a vehicle, and the conductive material contains at least one selected from the group consisting of, for example, Au, Ag, Cu, Ni, Pd, and Pt. Those are preferred. Although the thickness of the terminal electrodes 21 and 22 is suitably determined according to a use etc., it is 10-50 micrometers normally.

  Next, a preferred method for manufacturing the multilayer piezoelectric element 1 will be described with reference to FIG. FIG. 2 is a flowchart showing the manufacturing process of the multilayer piezoelectric element 1.

First, oxides such as PbO powder, ZrO ₂ powder, TiO ₂ powder, SrCO ₃ powder, Nb ₂ O ₅ powder and ZnO powder are prepared and weighed as starting materials for the main component (step S101). As a starting material, not an oxide but a material that becomes an oxide by firing, such as carbonate or oxalate, may be used. As these raw material powders, those having an average particle diameter of about 0.5 to 10 μm are usually used.

If necessary, starting materials for subcomponents are prepared and weighed (step S101). As a starting material for the auxiliary component, oxides such as Ta ₂ O ₅ powder, Sb ₂ O ₃ powder, NiO powder, CoO powder, Fe ₂ O ₃ powder, and CuO powder can be used. However, instead of an oxide, a material that becomes an oxide by firing, such as carbonate or oxalate, may be used. These subcomponents have the effect of improving the sinterability and lowering the firing temperature.

Subsequently, the starting materials of the main component and the subcomponent are wet pulverized and mixed using, for example, a ball mill to form a raw material mixture (step S102).
In addition, although the starting material of a subcomponent may be added before temporary baking (step S103) mentioned later, you may make it add after temporary baking. However, it is preferable to add it before calcination because a more uniform piezoelectric ceramic can be produced. When added after calcination, it is preferable to use an oxide as a starting material for the auxiliary component.

Next, the raw material mixture is dried and, for example, pre-baked at a temperature of 750 to 950 ° C. for 1 to 6 hours (step S103). This calcination may be performed in the air, or may be performed in an atmosphere having a higher oxygen partial pressure or in a pure oxygen atmosphere than in the air. After pre-baking, for example, this pre-fired product is wet pulverized and mixed with a ball mill to form a pre-baked powder containing a main component and, if necessary, subcomponents (step S104).
Next, a binder is added to the temporarily fired powder to produce a piezoelectric ceramic layer paste (step S105). Specifically, it is as follows. First, a slurry is obtained by wet pulverization using, for example, a ball mill. At this time, water or an alcohol such as ethanol, or a mixed solvent of water and ethanol can be used as a solvent for the slurry. The wet pulverization is preferably performed until the average particle size of the calcined powder becomes about 0.5 to 2.0 μm.

  The resulting slurry is then dispersed in an organic vehicle. The organic vehicle is obtained by dissolving a binder in an organic solvent, and the binder used in the organic vehicle is not particularly limited, and may be appropriately selected from usual various binders such as ethyl cellulose, polyvinyl butyral, and acrylic. Also, the organic solvent used at this time is not particularly limited, and may be appropriately selected from organic solvents such as terpineol, butyl carbitol, acetone, toluene, MEK (methyl ethyl ketone), terpineol, etc. Just choose.

  When the piezoelectric ceramic layer paste is used as a water-based paint, a water-based vehicle in which a water-soluble binder, a dispersant, or the like is dissolved in water and a pre-fired powder may be kneaded. The water-soluble binder used for the water-based vehicle is not particularly limited, and for example, polyvinyl alcohol, cellulose, water-soluble acrylic resin, or the like may be used.

Also, an internal electrode layer paste is prepared (step S106). The internal electrode layer paste is prepared by kneading the various conductive materials described above or various oxides, organometallic compounds, resinates, and the like, which become the conductive materials described above after firing, and the above-described organic vehicle.
Further, the terminal electrode paste is prepared in the same manner as the internal electrode layer paste (step S107).
In the above, the piezoelectric ceramic layer paste, the internal electrode layer paste, and the terminal electrode paste are produced in order, but it goes without saying that they may be produced in parallel or in the reverse order.

  The content of the organic vehicle in each paste is not particularly limited, and may be a normal content, for example, about 5 to 10% by weight for the binder and about 10 to 50% by weight for the solvent. Each paste may contain an additive selected from various dispersants, plasticizers, dielectrics, insulators and the like as necessary.

Next, a green chip (laminated body) to be fired is manufactured using the above paste (step S108).
When producing a green chip using a printing method, a piezoelectric ceramic layer paste is printed a plurality of times on a substrate such as polyethylene terephthalate with a predetermined thickness, and as shown in FIG. 11a is formed. Next, the internal electrode layer paste is printed in a predetermined pattern on the green outer piezoelectric ceramic layer 11a to form a green internal electrode layer (internal electrode layer precursor) 12a. Next, a piezoelectric ceramic layer paste (piezoelectric ceramic layer precursor) 11b is formed on the internal electrode layer 12a in the green state by printing the piezoelectric ceramic layer paste at a predetermined thickness a plurality of times in the same manner as described above. To do. Next, the internal electrode layer paste is printed in a predetermined pattern on the green piezoelectric ceramic layer 11b to form the green internal electrode layer 12b. The internal electrode layers 12a, 12b,... In the green state are formed so as to be opposed and exposed on different end surfaces. The above operation is repeated a predetermined number of times, and finally, the piezoelectric ceramic layer paste is printed a plurality of times at a predetermined thickness on the green internal electrode 12 to form the green external piezoelectric ceramic layer 11c. To do. Then, it pressurizes and pressure-bonds, heating, cut | disconnects to a predetermined shape, and is set as a green chip (laminated body).
In the above, an example in which a green chip is manufactured by a printing method has been described. However, a green chip can also be manufactured by using a sheet forming method.

Next, the binder removal process is performed on the green chip (step S109).
In the binder removal treatment, it is necessary to consider the oxidation of the conductive material in the internal electrode layer precursor, and heating in a reducing atmosphere should be employed. On the other hand, it is necessary to consider that the oxide contained in the piezoelectric ceramic layer precursor, such as PbO, is reduced in the binder removal process. This is because a sufficient amount of oxygen may not be supplied in the subsequent oxygen supply heat treatment depending on the degree of reduction. Therefore, for example, when Cu is used as the conductive material, the equilibrium oxygen partial pressure of Cu and Cu ₂ O (hereinafter simply referred to as equilibrium oxygen partial pressure of Cu) and the equilibrium oxygen partial pressure of Pb and PbO (hereinafter simply referred to as equilibrium oxygen of Pb). It is necessary to set what reducing atmosphere is applied to the binder removal process based on the partial pressure).

  FIG. 3 shows the equilibrium oxygen partial pressure of Cu and the equilibrium oxygen partial pressure of Pb. Theoretically, the binder removal treatment is performed with the oxygen partial pressure in the region surrounded by two curves indicating the oxygen partial pressure. If done, PbO is not reduced and Cu can be prevented from being oxidized. Since the binder removal treatment is preferably performed in a temperature range of 300 to 650 ° C., the atmosphere of the binder removal should be an oxygen partial pressure in a region where a chain line is hatched or in the vicinity thereof. If the temperature of the binder removal process is less than 300 ° C., the binder removal cannot be performed smoothly, and if it exceeds 650 ° C., the effect of the binder removal corresponding to the temperature cannot be obtained, resulting in 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. Further, the binder removal treatment can be performed independently of the firing and can be performed continuously with the firing. In the case where the firing is continuously performed, the binder removal process may be performed in the firing temperature increasing process.

After the binder removal process, firing (step S110) is performed. Firing is performed in a reducing atmosphere (first reducing atmosphere). This is for preventing or suppressing oxidation of base metal such as Cu used for the internal electrode 12. 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. As is apparent from FIG. 3, the firing is performed in an atmosphere having a higher oxygen partial pressure than the reducing atmosphere of the binder removal treatment, as the firing is performed at a higher temperature than the binder removal treatment. Since the firing is recommended to be performed in the range of 800 to 1080 ° C., the firing atmosphere should be an oxygen partial pressure in the vicinity of the hatched area or in the vicinity thereof. Specifically, a reducing atmosphere (first reducing atmosphere) having an oxygen partial pressure of 10 ⁻⁶ to 10 ⁻⁹ atm is preferable. This is because if the firing temperature is less than 800 ° C., a dense sintered body cannot be obtained, and if it exceeds 1080 ° C., the conductive material constituting the internal electrode 12 may be melted.

Next, according to the present invention, oxygen supply heat treatment is performed (step S111).
This heat treatment is performed in an atmosphere containing a predetermined oxygen for the purpose of preventing a decrease in the insulation resistance at a high temperature and obtaining a predetermined insulation resistance. The reason why the predetermined insulation resistance is obtained by this heat treatment is not clear, but the present inventors speculate that it is one or both of the following two reasons.
The first reason is that a predetermined insulation resistance can be obtained because the grain boundaries of the piezoelectric ceramic layer are insulated by the supply of oxygen.
As is well known, since SrTiO ₃ is difficult to be fired in the air, it is fired in a reducing atmosphere. At that time, the entire element body is reduced to become a ceramic semiconductor. The element body can be insulated by heat-treating (oxidizing) the element body in the atmosphere. In the structure after insulation, it is said that the crystal grains are semiconductors and the grain boundary portions are insulators. This is based on the theory that oxygen diffuses into the grain boundary to form a Schottky barrier by heat treatment in the atmosphere.
Since such grain boundary insulation also occurs in the present invention, a predetermined insulation resistance can be obtained.

Another reason is that the insulation resistance reduced by lattice defects can be improved by supplementing oxygen to lattice defects generated in the crystal grains of the piezoelectric ceramic layer by firing in a reducing atmosphere.
Further, as is well known, it has been confirmed that when a reduced baked product of BaTiO ₃ as a Ni base metal capacitor is heat-treated (oxidized) in the air, the transition loop that exists after calcination disappears. It has been clarified by TEM observation that this transition loop is a lattice defect. In the case of BaTiO ₃ , it is considered that the lattice defect is supplemented with oxygen by heat treatment.
In the piezoelectric ceramics examined by the present inventors, the above-described transition loop is not observed after firing. However, it is understood that the heat treatment according to the present invention has a function of complementing the lattice defects only when the transition loop is not observed.

If the atmosphere of this heat treatment contains excessive oxygen, the internal electrode 12 made of a base metal is oxidized, so it is necessary to regulate the contained oxygen. Based on the above considerations and the results of the examples described later, when manufacturing the laminated piezoelectric element 1 in which the internal electrode 12 is made of a base metal, the atmosphere of the heat treatment is oxygen of 10 ⁻² to 10 ⁻⁶ atm. A reducing atmosphere having a partial pressure (second reducing atmosphere) is used. The oxygen partial pressure is preferably 10 ⁻³ to 10 ⁻⁵ atm. Here, based on FIG. 3, when heat treatment is performed at this oxygen partial pressure, oxidation is caused when Cu is used as the internal electrode 12. However, the present inventors have confirmed that the internal electrode 12 is not oxidized to the inside even in the heat treatment at the oxygen partial pressure. FIG. 10 is a photomicrograph showing the peeled surface of the internal electrode 12 of the multilayer piezoelectric element 1 subjected to heat treatment according to the present invention, and FIG. 11 is the inside of the multilayer piezoelectric element 1 heat-treated in an atmosphere containing excess oxygen. It is a microscope picture which shows the peeling surface of the electrode 12. FIG. It can be seen that when the heat treatment is performed in an atmosphere containing excess oxygen, the surface of the internal electrode 12 becomes black and is oxidized. The oxygen partial pressure during the heat treatment may be constant or varied within the above range.

  Further, when the temperature of the heat treatment is low, it becomes difficult to supply oxygen to the grain boundaries and / or grains. On the other hand, if the temperature of the heat treatment is too high, the internal electrode 12 made of a base metal may be oxidized. Based on the above considerations and the results of Examples described later, when manufacturing the multilayer piezoelectric element 1 in which the internal electrode 12 is made of a base metal, the heat treatment temperature is set to 550 to 950 ° C. The heat treatment temperature is preferably 700 to 850 ° C. The temperature during the heat treatment may be constant or varied within the above range. Further, the temperature of this heat treatment is set to a temperature lower than the temperature of the preceding firing.

  The heat treatment time needs to be varied depending on the atmosphere (oxygen partial pressure) and temperature of the heat treatment, but if it is too short, oxygen cannot be supplied sufficiently. In addition, even if it takes longer than necessary, the effect is saturated and energy is wasted. Therefore, in the present invention, the heat treatment time is preferably 0.5 to 5 hours. A more preferable heat treatment time is 1 to 3 hours.

The above heat treatment for supplying oxygen can be performed independently of the firing, or can be performed continuously with the firing.
As shown in FIG. 4, the firing includes a temperature raising process, a holding process, and a temperature lowering process. However, when the oxygen supply heat treatment is performed independently of the firing, the temperature lowering process is completed as shown in FIG. Then, the temperature of the sintered body is raised again to the temperature of the heat treatment, and the temperature is lowered after being held for a predetermined time. This embodiment will normally be applied when firing and oxygen supply heat treatment are performed using separate heating furnaces.

  When the oxygen supply heat treatment is performed as one step of firing, a temperature lowering process of firing is used as shown in FIG. That is, as shown in FIG. 5, the oxygen supply heat treatment can be performed by holding the temperature for a predetermined time in the temperature range of the oxygen supply heat treatment in the temperature lowering process of firing. After holding for a predetermined time, the temperature may be lowered in the same manner as the temperature lowering process of firing. Note that since the atmosphere of the firing and the oxygen supply heat treatment is as described above, it is necessary to change from the firing atmosphere to the oxygen supply heat treatment atmosphere at least before reaching the temperature range of the oxygen supply heat treatment. According to this aspect, the firing and the oxygen supply heat treatment can be performed using the same heating furnace.

The laminated body 10 manufactured through the above steps is subjected to end face polishing by, for example, barrel polishing or sand blasting, and the terminal electrodes 21 and 22 are formed by printing or baking the above-described terminal electrode paste (step S112). In addition to printing or baking, the terminal electrodes 21 and 22 can also be formed by sputtering.
As described above, the multilayer piezoelectric element 1 shown in FIG. 1 is obtained.

Hereinafter, the present invention will be described based on specific examples.
PbO powder, SrCO ₃ powder, ZnO powder, Nb ₂ O ₅ powder, TiO ₂ powder and ZrO ₂ powder are weighed to have the following main composition, and Ta ₂ O ₅ powder is added as an auxiliary component to the main component. The raw material powder to which .4% by weight was added was wet mixed by a ball mill for 16 hours, dried, and then calcined at 700 to 900 ° C. for 2 hours in an air atmosphere. The obtained calcined powder was further wet pulverized by a ball mill for 16 hours, dried, and granulated by adding an appropriate amount of polyvinyl alcohol (PVA) as a binder. As the granulated powder, a disk-shaped molded body having a diameter of 17 mmφ and a thickness of 1 mm was produced at a pressure of 245 MPa using a uniaxial press molding machine.
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 molded sample was debindered at 600 ° C.-8 hr in an atmosphere having an oxygen partial pressure of 4 × 10 ⁻¹⁵ atm, and then fired at 1020 ° C.-2 hr in an atmosphere having an oxygen partial pressure of 1 × 10 ⁻⁸ atm. Furthermore, this fired body was heat-treated at 600 to 1020 ° C. in an atmosphere having an oxygen partial pressure of 10 ⁻¹ to 10 ⁻⁷ atm. Thereafter, a disk having a thickness of 0.6 mm was obtained by lapping. Ag paste was applied to both sides of this disk and baked at 300 ° C. for 20 minutes.
Thereafter, polarization treatment was performed at 3 kV / mm-15 min in 120 ° C. silicone oil. This sample was allowed to stand for 10 minutes in a constant temperature bath at 50 ° C., 100 ° C., and 150 ° C., and then a voltage of 600 V was charged for 30 seconds to measure insulation resistance (IR). The results are shown in FIG. 6 to FIG. 9, and it can be seen that the insulation resistance (IR) tends to decrease as the temperature of the standing is increased.

Further, the calcined and pulverized powder was mixed with a binder, a solvent, and the like to make a slurry, and a green sheet was formed by a doctor blade method. A conductive paste containing Cu particles was printed on the green sheet to form an internal electrode layer precursor. After printing, 300 green sheets were laminated and thermocompression bonded at 80 ° C. and 1 ton / cm ² to obtain a green chip. After cutting this green chip into a product size and removing the binder at 550 ° C.-32 hr in an atmosphere where the oxygen partial pressure is 4.8 × 10 ⁻¹⁶ atm, the oxygen partial pressure is 1.7 × 10 ⁻⁸ atm. 950 ℃ -2hr atmosphere, an oxygen partial pressure of 1.4 × 10 ^-8 atm in the atmosphere 980 ℃ -2hr, the oxygen partial pressure was 1020 ℃ -2hr firing in an atmosphere of 1.3 × 10 ^-8 atm. This sintered body was heat-treated at 600 to 1020 ° C. in a reducing atmosphere having an oxygen partial pressure of 10 ⁻¹ to 10 ⁻⁷ atm.
Thereafter, Cu and Ag were formed by vapor deposition on both sides of the laminate, and subjected to a polarization treatment of 2.5 kV / mm-5 min in 150 ° C. silicone oil. Displacement measurement was performed by applying a voltage of 2 kV / mm-0.1 Hz to this sample. If there was a displacement, it was determined that the internal electrode layer made of Cu was not oxidized. It was judged that the electrode layer was oxidized.

Table 1 shows the insulation resistance (IR) at 150 ° C. and the oxidation state of the internal electrode (Cu) in the sintered body under each heat treatment condition.
Sample No. 17 is a conventional condition of firing in a reducing atmosphere. Under this condition, Cu oxidation of the laminate is not observed, but the insulation resistance (IR) at 150 ° C. is significantly lower than 10 ¹² Ω · cm.
Sample No. 18 was fired in the air, but contrary to firing in a reducing atmosphere, although the insulation resistance (IR) at 150 ° C. was sufficient, oxidation was observed on the Cu electrode of the laminate.

Next, Sample No. with a heat treatment temperature of 600 ° C was used. For Samples Nos. 1, 5, 9, and 13, the insulation resistance (IR) at 150 ° C. is less than 10 ¹² Ω · cm, and the heat treatment temperature is 1020 ° C. For all of 4, 8, 12, and 16, Cu oxidation of the laminate is observed.
Sample No. 2 having an oxygen partial pressure of 2 × 10 ⁻⁷ atm was used. For Nos. 1, 2, 3, and 4, No. 1020 ° C. heat treatment No. Except for sample No. 4, the insulation resistance (IR) at 150 ° C. is less than 10 ¹² Ω · cm, and the sample partial No. is 2 × 10 ⁻¹ atm (atmosphere). In all of 13, 14, 15, and 16, Cu oxidation of the laminate is observed.
The insulation resistance (IR) at 150 ° C. is 10 ¹² Ω · cm or more, and Cu oxidation is not observed in the laminate. 6, 7, 10, and 11. In these samples, the conductivity of Cu was substantially maintained from firing to heat treatment. This also means that the function of the internal electrode made of Cu is ensured. Further, from the results of Table 1, the heat treatment conditions are 650 to 950 ° C., preferably 700 to 800 ° C. in an atmosphere having an oxygen partial pressure of 10 ⁻² to 10 ⁻⁶ atm, preferably 10 ⁻³ to 10 ⁻⁵ atm. This suggests that the temperature range should be adopted.

Insulation resistance (IR) at 150 ° C. of the fired body in the same manner as in Example 1 except that 0.4% by weight of Ta ₂ O ₅ powder and 0.05% by weight of CoO powder were added as subcomponents to the following main components. ) And the oxidation state of the internal electrode (Cu) in the laminate was observed. The results are shown in Table 2.
Main component: (Pb _0.965 Sr _0.03 ) [(Zn _1/3 Nb _2/3 ) _0.1 Ti _0.43 Zr _0.47 ] O ₃

Sample No. with a heat treatment temperature of 500 ° C. For samples 20, 25, 30, and 35, the insulation resistance (IR) at 150 ° C. is less than 10 ¹² Ω · cm, and the heat treatment temperature is 1020 ° C. As for 24, 29, 34 and 39, Cu oxidation of the laminated body is observed.
Sample No. 2 having an oxygen partial pressure of 2 × 10 ⁻⁷ atm was used. For Nos. 20-24, No. 1020 ° C. heat treatment No. Except for Sample No. 24, the insulation resistance (IR) at 150 ° C. was less than 10 ¹² Ω · cm, and the sample partial No. was 2 × 10 ⁻¹ atm (atmosphere). About 36-39, Cu oxidation of a laminated body is seen.
The insulation resistance (IR) at 150 ° C. is 10 ¹² Ω · cm or more, and Cu oxidation is not observed in the laminate. 26, 27, 28, 31, 32, 33. In these samples, the conductivity of Cu was substantially maintained from firing to heat treatment. This also means that the function of the internal electrode made of Cu is ensured. Further, from the results of Table 2, the heat treatment conditions for the composition of this example are 550 to 950 ° C., preferably in an atmosphere with an oxygen partial pressure of 10 ⁻² to 10 ⁻⁶ atm, preferably 10 ⁻³ to 10 ⁻⁵ atm. Suggests that a temperature range of 600-800 ° C. should be employed.

It is a figure which shows one structural example of the lamination type piezoelectric element in this Embodiment. It is a flowchart which shows the manufacture procedure of the lamination type piezoelectric element in this Embodiment. It is a graph showing a relationship between Cu and Cu ₂ O equilibrium oxygen partial pressure and the temperature of the equilibrium oxygen partial pressure and Pb and PbO of. It is a figure which shows the relationship between the baking in this Embodiment, and oxygen supply heat processing. It is a figure which shows the relationship between the baking in this Embodiment, and oxygen supply heat processing. It is a graph which shows the relationship between the insulation resistance (IR) and temperature which were measured in the Example (oxygen partial pressure of oxygen supply heat processing: 2 * 10 < ^-7 > atm). It is a graph which shows the relationship between the insulation resistance (IR) and temperature which were measured in the Example (oxygen partial pressure of oxygen supply heat processing: 2 * 10 < ^-5 > atm). It is a graph which shows the relationship between the insulation resistance (IR) and temperature which were measured in the Example (oxygen partial pressure of oxygen supply heat processing: 2 * 10 < ^-3 > atm). It is a graph which shows the relationship between the insulation resistance (IR) and temperature which were measured in the Example (oxygen partial pressure of oxygen supply heat processing: 2 * 10 < ^-1 > atm). It is a microscope picture which shows the peeling surface of the internal electrode of the laminated piezoelectric element which performed the heat processing according to this invention. It is a microscope picture which shows the peeling surface of the internal electrode of the lamination type piezoelectric element heat-processed in the atmosphere containing excess oxygen.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Laminated piezoelectric element, 10 ... Laminated body, 11 ... Piezoelectric ceramic layer, 12 ... Internal electrode, 21, 22 ... Terminal electrode

Claims (4)

A method of manufacturing a laminated piezoelectric element in which a piezoelectric ceramic layer and internal electrodes are laminated,
A firing step of firing a laminate in which a piezoelectric ceramic layer precursor containing a ceramic composition powder of a predetermined composition and an internal electrode precursor containing Cu as a base metal as a conductive material are laminated in a first reducing atmosphere;
A heat treatment step of heating the fired laminated body in a second reducing atmosphere having a higher oxygen partial pressure than the first reducing atmosphere;
With
The piezoelectric ceramic layer is made of a Pb-based piezoelectric material,
The first reducing atmosphere has an oxygen partial pressure of 10 ⁻⁶ to 10 ⁻⁹ atm, and the second reducing atmosphere has an oxygen partial pressure of 10 ⁻² to 10 ⁻⁶ atm,
A method for manufacturing a multilayer piezoelectric element, wherein a heating temperature T1 in the firing step is 800 to 1080 ° C., and a heating temperature T2 in the heat treatment step is 550 to 950 ° C. (where T1> T2). 2. The heat treatment step according to claim 1, wherein the second reducing atmosphere has an oxygen partial pressure of 10 ⁻³ to 10 ⁻⁵ atm and a heating temperature T 2 of 700 to 850 ° C. 3. A method for manufacturing a laminated piezoelectric element.   The method for manufacturing a multilayer piezoelectric element according to claim 1 or 2, wherein the conductivity of the conductive material is substantially maintained from the firing step to the heat treatment step.   The method for manufacturing a multilayer piezoelectric element according to any one of claims 1 to 3, wherein oxygen is supplied into the piezoelectric ceramic layer in the heat treatment step.

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