JP4066432B2 - Manufacturing method of laminated piezoelectric ceramic element - Google Patents

Description

The present invention relates to a method for manufacturing a laminated piezoelectric ceramic element suitable for a laminated piezoelectric sensor that detects a stress from the outside and generates a voltage, a laminated piezoelectric actuator that generates a displacement and a force by applying a voltage, and the like. a method of manufacturing a multilayer piezoelectric ceramic element using the base metal in the electrode.

  Usually, a laminated piezoelectric ceramic element is formed by integrating a plurality of piezoelectric ceramic plates mainly composed of lead zirconate titanate and an internal electrode plate made of a noble metal such as an Ag-Pd alloy, and the internal electrodes become a counter electrode one by one. In this structure, the layers are connected to a pair of common external electrodes, and an unsintered laminate is formed by a thick film printing lamination method called a green sheet method, and the binder removal step and the sintering step are performed in the atmosphere. It is common.

  The binder removal step described above is a step of removing organic substances such as a binder contained in the unsintered laminate at a temperature of about 500 ° C., and the sintering step of lead zirconate titanate ceramics is about 950 ° C. to 1200 ° C. Become temperature. In order to form a plate-like electrode without oxidizing the internal electrode in such a binder removal process or sintering process, it was necessary to use a noble metal such as an Ag—Pd alloy as the internal electrode.

  The production of Pd in the internal electrode is unevenly distributed on the earth, is expensive, has a large price fluctuation, and the cost of Pd in the material cost of the multilayer piezoelectric ceramic element is large. Has the problem of reducing the cost of the internal electrodes.

  In order to reduce the cost of the internal electrode, the internal electrode material may be a base metal. However, base metals such as Cu, Ni, and W are easily oxidized during the sintering process unlike noble metals, so it is necessary to sinter in a low oxygen partial pressure atmosphere, but lead oxide is the main component in the low oxygen atmosphere. Since the piezoelectric ceramic is easily reduced, there is a problem that adjustment of the sintering atmosphere is very difficult.

As a similar technology, in recent years, products using Ni as an internal electrode have been developed and commercialized for multilayer ceramic capacitors mainly composed of dielectric ceramics BaTiO _{3. In} this case, the binder removal process is performed in the atmosphere, etc. When this was performed in an atmosphere under a high oxygen partial pressure, since the Ni internal electrode oxidatively expanded, stress was generated inside the multilayer ceramic capacitor, causing delamination and cracks during sintering.

Therefore, it has been proposed to use CuO or Cu ₂ O instead of Ni as the internal electrode material to prevent oxidative expansion of the internal electrode during debinding. In this case, it is necessary to reduce the internal electrode to Cu after debinding, but if the reduction is insufficient, a part of the internal electrode remains CuO and diffuses into the ceramic during sintering, There is a problem that causes deterioration of insulation resistance and dielectric characteristics.

  In order to solve such a problem, in Patent Document 1, after the binder component is removed, the dielectric ceramic and the internal electrode are reduced together, and the internal electrode is not oxidized after the reduction step. There has been proposed a manufacturing method including a step of firing in an atmosphere in which ceramics are oxidized.

In this method, after reducing the BaTiO ₃ dielectric ceramics and internal electrodes in a reducing atmosphere, only the dielectric ceramics are reoxidized. However, when reduction treatment is performed on piezoelectric ceramics containing lead oxide, such as lead zirconate titanate, lead oxide is reduced to a liquid phase of metallic lead, and the metallic lead in the liquid phase is sintered due to surface energy. If it is aggregated inside the body or deposited on the surface of the sintered body and further reoxidation treatment is performed, the composition of the piezoelectric ceramic becomes non-uniform and piezoelectric properties cannot be obtained. Is possible.

JP-A-5-82387

  As described above, in a laminated piezoelectric ceramic element using a base metal internal electrode for cost reduction, the internal electrode oxidizes and expands during the sintering process. There is a problem that delamination and cracks occur, and a lead-zirconate titanate-based piezoelectric ceramic has a problem that the reduction-reoxidation process cannot be applied because lead oxide is reduced.

Accordingly, the present invention uses a base metal internal electrodes, without delamination, the piezoelectric characteristics are good, and easy adjustment of the atmosphere sintering, to realize a method for manufacturing inexpensive multilayer piezoelectric ceramic element It is intended.

According to the present invention, a laminated body in which a plurality of piezoelectric ceramic layers and internal electrode layers are alternately laminated and integrated, and an external electrode that is electrically connected to the internal electrode is formed on a surface exposed portion of the internal electrode layer. In the laminated piezoelectric ceramic element manufacturing method , the internal electrode is mainly composed of Cu, and at least one metal of Ni, Ir, Pd, Pt, and Rh is 0.5 wt% or more, 10 wt% or less, It is a manufacturing method of the lamination type piezoelectric ceramic element to be contained, Comprising: The average particle diameter of the metal powder contained in the electrically conductive paste which prints the internal electrode is 0.1-5 micrometers, and the surface of the metal powder is PbO, _{Bi 2 O 3, SiO 2,} GeO 2, Li 2 CO 3, ZnO, B 2 O 3, BaO, SrO, CaO, CuO, to form a low melting point of the inorganic thin layer consisting of at least one or more of Ag Method of fabricating the multilayer piezoelectric ceramic element, characterized in that is obtained.

Further, according to the present invention, the inorganic thin film layer formed on the surface of the metal powder has a melting point at 1000 ° C. or less, the thickness of the multilayer piezoelectric ceramic element, characterized in that at 10nm or more A manufacturing method is obtained.

Further, according to the present invention, the content of the inorganic thin film layer formed on the surface of the metal powder, the metal powder to 0.5 wt% or more, above the multilayer, characterized in that 5 wt% or less A method for manufacturing a piezoelectric ceramic element is obtained.

According to the invention, the piezoelectric ceramic raw material powder forming the piezoelectric ceramic layer contains a compound comprising the same element as the inorganic thin film layer in an amount of 0.1 wt% or more and 2 wt% or less. The method for producing the laminated piezoelectric ceramic element is obtained.

Further, according to the present invention, when the temperature is 950 ° C., the oxygen partial pressure is 1.01 × 10 ³ to 1.01 × 10 ² Pa, and when the temperature is 1050 ° C., the oxygen partial pressure is 7.07 × 10 ⁻² to 2.02 ×. It is possible to obtain the method for producing a laminated piezoelectric ceramic element as described above, wherein sintering is performed in an atmosphere in a range of 10 ⁻¹ Pa.

According to the present invention, by adding an alloy component or forming an inorganic thin film layer to Cu powder for internal electrodes, sintering is performed at a temperature of 950 ° C. to 1050 ° C., there is no delamination, and the piezoelectric characteristics are good. no oxidation of the internal electrode in the binder process, it is possible to provide a method for manufacturing inexpensive multilayer piezoelectric ceramic element is no reduction of the piezoelectric ceramic in a reducing atmosphere.

  Hereinafter, embodiments of the present invention will be described based on examples.

The main component is a piezoelectric ceramic powder having a chemical composition of 0.5 Pb (Ni _1/3 Nb _2/3 ) O ₃ -0.15PbZrO ₃ -0.35PbTiO ₃ , and 5 mol of PbO as a low temperature sintering aid. % Was added. Next, this powder and polyvinyl butyral (PVB) as an organic binder, ethylene glycol ethyl ether solvent as a dispersing agent, and dibutyl phthalate as a plasticizer are weighed in amounts shown in Table 1, kneaded with a homomixer to form a slurry, and a doctor blade A green sheet having a thickness of 110 μm was prepared by the method.

  The conductive paste was prepared by using a Cu alloy powder having an average particle diameter of 3 μm to which 10% by weight of Ni was added, and weighing and weighing ethylcellulose-α terpineol-based organic vehicle as shown in Table 2, and kneading with a three-roll mill. Using this conductive paste, a plurality of internal electrode patterns having dimensions of 6 mm to 6 mm and a thickness of 6 μm were printed on the green sheet by screen printing.

  Next, the green sheet on which the internal electrode pattern is printed is cut to a size of 6.5 mm to 7 mm, and 100 sheets are stacked in the mold so that each internal electrode becomes a counter electrode, and the temperature is 150 ° C. and the pressure is 24. It was hot-pressed at 5 MPa to obtain a green laminate. Thereafter, the green laminate was debindered by controlling the temperature-atmosphere in the temperature range of 250 to 600 ° C. in air and nitrogen. FIG. 1A shows a temperature-atmosphere profile of the binder removal. Next, the temperature and atmosphere were automatically controlled and sintered at a temperature of 1050 ° C. for 2 hours to form a laminated piezoelectric ceramic element, and an Ag external electrode connected to the internal electrode exposed at the end face. The performance of the obtained multilayer piezoelectric ceramic element is shown in Table 3. For comparison, a laminated piezoelectric ceramic element having the same structure was manufactured using the same piezoelectric ceramic powder and an alloy of Ag 70 wt% -Pd 30 wt% for the internal electrode, and the performance is shown in Table 3.

  FIG. 2 shows the temperature-oxygen partial pressure range of automatic control during sintering according to the present invention.

  In this example, a piezoelectric ceramic mainly composed of lead oxide, which has a sintering temperature of 1050 ° C. and is relatively easy to be reduced under a low oxygen partial pressure, was used as the piezoelectric ceramic. Although an alloy is used, the same effect can be obtained as long as it is at least one metal selected from Ir, Pd, Pt, and Rh other than a metal that dissolves in Cu and has a high melting point, for example, Ni. However, if the amount is less than 0.5% by weight, the effect of increasing the melting point is small, and if it exceeds 10% by weight, the melting point becomes too high and the internal electrode becomes insufficiently sintered. 0.5 to 10% by weight is suitable.

  In addition, when the particle size of the alloy powder is less than 0.1 μm, the surface oxidation proceeds spontaneously, the conductive paste cannot be produced, and the thickness of the internal electrode after sintering is 3 to 5 μm. Therefore, if the particle diameter of the alloy powder exceeds 5 μm, the thickness of the internal electrode after sintering also exceeds 5 μm, so the average particle diameter of the metal powder contained in the conductive paste is suitably 0.1 to 5 μm.

Using the same piezoelectric ceramic powder as in Example 1, the metal powder forming the internal electrode was a Cu powder in which a compound composed of Bi ₂ O ₃ , SiO ₂ and BaO was formed on the surface of the Cu powder. An unsintered laminated piezoelectric ceramic element having the same structure as 1 was manufactured.

A method of forming a compound of Bi ₂ O ₃ , SiO _2, and BaO on Cu powder uses metal alkoxide as a starting material, dissolves these in 2 methoxyethanol in a nitrogen atmosphere, and selectively forms on the Cu powder surface. An inorganic thin film layer having a thickness of 15 nm was formed on the surface of the Cu powder by forming the surface by a surface modification method using a sol-gel method for hydrolysis, followed by heat treatment at 250 ° C. in a reducing atmosphere. FIG. 3 shows a cross-sectional view of Cu powder on which an inorganic thin film layer is formed.

FIG. 4A shows the thermal analysis result of the Cu powder, and FIG. 4B shows the thermal analysis result of the Cu powder on which the inorganic thin film layer is formed. From FIG. 4A, the Cu powder becomes Cu ₂ O at about 200 ° C. in the atmosphere and becomes CuO at about 330 ° C. From FIG. 4B, the Cu powder with the inorganic thin film layer formed in the atmosphere As can be seen from FIG. Therefore, it can be seen that the unsintered laminated piezoelectric ceramic element using Cu powder with an inorganic thin film layer as an internal electrode can be debindered even at 300 ° C. in the atmosphere.

  In this example, this unsintered laminate was debindered in the atmosphere and nitrogen at a temperature range of 250 to 600 ° C. with an atmosphere profile as shown in FIG. 1B, and then the hatched portion in FIG. Sintering was performed at a temperature of 1000 ° C. for 2 hours in an atmosphere so as to be within the range of the oxygen partial pressure, to form a laminated piezoelectric ceramic element, and an Ag external electrode connected to the internal electrode exposed at the end face was formed. The performance of the obtained multilayer piezoelectric ceramic element is shown in Table 3.

An inorganic thin film layer having a melting point of 1000 ° C. or lower during sintering at 1000 ° C. becomes a liquid phase and precipitates at the interface between the piezoelectric ceramic layer and the internal electrode layer and eventually reacts or diffuses with the piezoelectric ceramic layer. It is necessary to use a compound that does not degrade the piezoelectric characteristics even when it reacts with piezoelectric ceramics. Other than Bi ₂ O ₃ —SiO ₂ —BaO compounds, PbO, Bi ₂ O ₃ , SiO ₂ , GeO ₂ , Li ₂ CO The same effect can be obtained with a low melting point oxide containing at least one of ₃ , ZnO, B ₂ O ₃ , BaO, SrO, CaO and CuO, and the same effect can be obtained with Ag.

FIG. 5 shows the thickness of the Bi ₂ O ₃ —SiO ₂ —BaO inorganic thin film layer and the oxidation temperature of the Cu powder. FIG. 5 shows that when the thickness of the inorganic thin film layer is less than 10 nm, the inorganic thin film layer cannot be formed on the entire surface of the Cu powder and is partially oxidized. By setting the thickness of the inorganic thin film layer to 10 nm or more, the inorganic thin film layer is uniformly formed on the surface of the Cu powder, and the oxidation start temperature of the Cu powder becomes 300 ° C. or higher. It is possible to set the temperature to 0 ° C., and the removal of organic components is complete, and a dense sintered body can be obtained.

  FIG. 6 shows the particle diameter of the Cu powder and the content of the inorganic thin film layer when the 10 nm inorganic thin film layer was formed. Since the thickness of the internal electrode of the laminated body after sintering is suitably 1 to 5 μm, the particle diameter of the Cu powder is preferably 3 μm or less. In addition, if the content of the inorganic thin film layer is less than 0.5% by weight, the particle diameter of the Cu powder exceeds 5 μm, so the content of the inorganic thin film layer is required to be 0.5% by weight or more. If the content is large, the component of the inorganic thin film compound reacts with Cu and the piezoelectric ceramic layer during sintering, and the electrical resistance and piezoelectric characteristics deteriorate, so the content of the inorganic thin film layer is 5 wt.% With respect to the Cu powder. % Or less is preferred.

A powder obtained by adding 2% by weight of a compound composed of Bi ₂ O ₃ , SiO ₂ and BaO to the same piezoelectric ceramic powder as in Example 1 was used as a starting material, and the metal powder forming the internal electrode was on the surface of the Cu powder. Using Cu powder in which a compound composed of Bi ₂ O ₃ , SiO ₂ and BaO was formed, the binder was removed under the same conditions as in Example 2, and then within the range of the oxygen partial pressure in the shaded area in FIG. Sintering was performed in an atmosphere at a temperature of 950 ° C. for 2 hours to produce a laminated piezoelectric ceramic element having the same structure as in Example 1.

  Compared to Example 1, Example 2 and Example 3 have lower sintering temperatures of 50 ° C. and 100 ° C., respectively, because the low melting point compound serves as a sintering aid and sintering at a lower temperature. This is because the densification proceeds.

When an inorganic thin film layer of a compound composed of Bi ₂ O ₃ , SiO _2, and BaO on the surface of the Cu powder becomes a liquid phase during sintering and diffuses or reacts with the piezoelectric ceramic layer, a concentration gradient is generated. By adding 0.1 to 2% by weight of the compound containing the same element as the inorganic thin film layer to the ceramic raw material powder, the concentration gradient between the internal electrode and the piezoelectric ceramic can be reduced. An element can be manufactured. If the amount of the compound containing the same element as the inorganic thin film layer to the piezoelectric ceramic raw material powder is less than 0.1% by weight, the concentration gradient reduction effect cannot be obtained, and if it exceeds 2% by weight, the amount of the liquid phase increases. It reacts too much with the piezoelectric ceramic, and the piezoelectric ceramic is altered and the electrical characteristics are lowered. The performance of the obtained multilayer piezoelectric ceramic element is shown in Table 3.

Using the same piezoelectric ceramic powder as in Example 1, the metal powder forming the internal electrode was a Cu powder in which a compound composed of Bi ₂ O ₃ , SiO ₂ and BaO was formed on the surface of the Cu powder. An unsintered laminated piezoelectric ceramic element having the same structure as 1 was manufactured.

In this embodiment, lead oxide ceramics are used as piezoelectric ceramics and Cu is used as internal electrodes. Therefore, lead oxide is not reduced in the sintering process, and sintering in an oxygen partial pressure atmosphere in which Cu internal electrodes are not oxidized is performed. When the temperature is 950 ° C., the oxygen partial pressure is 1.01 × 10 ³ to 1.01 × 10 ² Pa. At 1050 ° C., the oxygen partial pressure is 7.07 × 10 ⁻² to 2.02 × 10 ⁻¹ Pa. Sintered in a range of atmospheres. If the oxygen partial pressure is higher than this atmospheric range, the Cu internal electrode is oxidized, and if it is lower, lead oxide is reduced, so that the electrical characteristics as a multilayer piezoelectric ceramic element cannot be obtained.

  The performance of the obtained multilayer piezoelectric ceramic element is shown in Table 3.

  From Table 3, the performance of the laminated piezoelectric ceramic elements obtained in Examples 1 to 4 of the present invention is comparable to the comparative example in which noble metal is used for the internal electrode, and the cost of the internal electrode is that of the comparative example. It can be seen that the ratio is reduced from 1/3 to 1/7.

The figure which shows the temperature-atmosphere profile of a binder removal. FIG. 1A shows the temperature-atmosphere profile of the binder removed in Example 1 of the present invention, and FIG. 1B shows the temperature-atmosphere profile of the binder removed in Example 2 of the present invention. Temperature-oxygen partial pressure range of automatic control during sintering of the present invention. Sectional drawing of Cu powder in which the inorganic thin film layer of this invention was formed. The figure which shows the thermal-analysis result of Cu powder which formed Cu powder and the inorganic thin film layer. FIG. 4A is a diagram showing a thermal analysis result of Cu powder, and FIG. 4B is a diagram showing a thermal analysis result of Cu powder on which an inorganic thin film layer is formed. It shows the thickness, the relationship between the oxidation temperature of Cu powder Bi ₂ O ₃ -SiO ₂ -BaO inorganic thin layer. The figure which shows the relationship between the particle diameter of Cu powder when forming a 10 nm inorganic thin film layer, and content of an inorganic thin film layer.

Explanation of symbols

31 Cu powder 32 Inorganic thin film layer

Claims (5)

A multilayer piezoelectric ceramic element in which a plurality of piezoelectric ceramic layers and internal electrode layers are alternately laminated and integrated, and an external electrode electrically connected to the internal electrode is formed on the exposed surface of the internal electrode layer in the method of manufacturing, the internal electrode is mainly composed of Cu, Ni, Ir, Pd, Pt, at least one metal of 0.5 wt% or more of Rh, 10 wt% or less, the laminated piezoelectric ceramics containing In the device manufacturing method, the average particle diameter of the metal powder contained in the conductive paste for printing the internal electrode is 0.1 to 5 μm, and PbO, Bi ₂ O ₃ , SiO on the surface of the metal powder. _{2, GeO 2, Li 2 CO} 3, ZnO, B 2 O 3, BaO, be SrO, CaO, CuO, characterized in that the formation of the low-melting inorganic thin layer consisting of at least one or more of Ag Method for producing a product layer piezoelectric ceramic element. 2. The method for manufacturing a multilayer piezoelectric ceramic element according to claim 1 , wherein the inorganic thin film layer formed on the surface of the metal powder has a melting point of 1000 ° C. or less and a thickness of 10 nm or more. The multilayer piezoelectric ceramic according to claim 1 or 2 , wherein the content of the inorganic thin film layer formed on the surface of the metal powder is 0.5 wt% or more and 5 wt% or less with respect to the metal powder. Device manufacturing method . A piezoelectric ceramic material powder for forming the piezoelectric ceramic layer, a compound having the same elements as the inorganic thin layer, 0.1 wt% or more, 2% by weight, of claims 1 to 3, characterized in that it contains A method for producing a multilayer piezoelectric ceramic element according to any one of the above. When the temperature is 950 ° C., the oxygen partial pressure is 1.01 × 10 ³ to 1.01 × 10 ² Pa, and when the temperature is 1050 ° C., the oxygen partial pressure is 7.07 × 10 ⁻² to 2.02 × 10 ⁻¹ Pa. 5. The method for manufacturing a laminated piezoelectric ceramic element according to claim 1, wherein the method is sintered at a temperature.

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