JP2006203242A - Method for manufacturing ceramic laminate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a ceramic laminate without the need for strictly controlling an oxygen partial pressure in a firing atmosphere. <P>SOLUTION: A method for manufacturing a ceramic laminate which is formed by alternately laminating a dielectric layer and an electrode layer comprises the steps of: preparing an unfired laminate which is formed by alternately laminating a unfired dielectric layer containing a PZT-based dielectric material and a unfired electrode layer containing an electrode material; feeding the unfired laminate into a firing chamber; evacuating the firing chamber; introducing atmospheric gas into the firing chamber as to meet a predetermined oxygen partial pressure; and firing the laminate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a ceramic laminate in which dielectric layers and electrode layers are alternately laminated.

  Piezo-actuators with simultaneously fired electrodes have been developed as injector drive elements for diesel engines and displacement elements for various positioning devices. The piezoelectric actuator has a configuration in which a pair of external electrodes is provided on a ceramic laminate in which dielectric layers and electrode layers are alternately laminated. The ceramic laminate has alternating unfired dielectric layers and unfired electrode layers. It manufactures by baking the laminated | stacked unbaking laminated body.

A PZT material that has been conventionally used as a dielectric layer of a ceramic laminate requires a firing temperature of about 1100 ° C. For this reason, an expensive noble metal such as Pd has to be used for the electrode layer with respect to the ceramic laminate of the dielectric layer using the PZT material. In order to reduce the cost, a PZT material that can be fired at 950 ° C. or lower has been developed, and a ceramic laminate using a base metal such as Cu for the electrode layer has been proposed. (Patent Document 1)
JP2002260951

  However, in the prior art disclosed in Patent Document 1, a base metal such as Cu is more easily oxidized than a noble metal such as Pd. Therefore, when fired in the atmosphere, it is oxidized to Cu oxide, and there is a problem that it becomes difficult to obtain desired electrical characteristics due to high specific resistance. Further, when Cu becomes a Cu oxide, there is a problem that the electrode layer is peeled off due to volume expansion.

  On the other hand, if the oxygen partial pressure in the firing atmosphere is low, Cu oxidation can be prevented, but the interface between the electrode layer and the dielectric layer adjacent to the electrode layer becomes insufficient, and the gap between the electrode layer and the dielectric layer is insufficient. Sometimes peeling occurred. Another problem is that the dielectric layer is reduced to produce metal Pb, which reacts with Cu in the electrode layer to melt out the electrode layer. When the electrode layer is melted, the electrode layer of the ceramic laminate may have an island shape, which may prevent the dielectric layer from functioning as a voltage application electrode.

  In order to prevent these problems, it is necessary to strictly control the oxygen partial pressure in the firing atmosphere, for example, by using a gas system having a complicated composition when firing the unfired laminate. That is, the firing atmosphere must be controlled to an oxygen partial pressure that does not reduce PZT or the like of the dielectric layer and does not oxidize Cu or the like of the electrode layer.

  In order to satisfy the above conditions, various gases are used, and the firing atmosphere is controlled within the shaded region in FIG. There is a need to. In other words, it was necessary to perform firing at an oxygen partial pressure corresponding to the temperature, the manufacturing process was very complicated, control was troublesome, and labor was required. Even if the cost of the electrode layer is reduced, there is a problem that the manufacturing process increases. Further, since the control is troublesome, a defective ceramic laminate is likely to be generated, and the manufacturing method has a low yield rate.

  The above problems are not limited to ceramic laminates used for actuators, but are used for ceramic capacitors, multilayer substrates, etc., and ceramic laminates that include PbO as the dielectric layer and electrode layers that easily oxidize such as Cu. The same applies to the body.

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a method for manufacturing a ceramic laminate that does not require strict control of the oxygen partial pressure in a firing atmosphere.

  In producing a ceramic laminate in which dielectric layers and electrode layers are alternately laminated, the present invention provides an unfired in which unfired dielectric layers containing PZT-based dielectric materials and unfired electrode layers containing electrode materials are alternately laminated. A laminate is prepared, the unfired laminate is introduced into a firing container, the inside of the firing container is evacuated, an atmospheric gas is introduced so as to have a predetermined oxygen partial pressure, and then firing is performed. It exists in the manufacturing method of a ceramic laminated body.

  Since the atmosphere gas is introduced so that a predetermined oxygen partial pressure is obtained after the inside of the firing container is once evacuated, it is easy to adjust the oxygen partial pressure. Furthermore, because the firing atmosphere in the firing container is unlikely to cause gas exchange with the outside, the firing atmosphere around the unfired laminate is naturally due to the absorption of oxygen accompanying the oxidation of the electrode layer and the release of oxygen accompanying the reduction of the dielectric layer. The atmosphere becomes an oxygen partial pressure in which the electrode layer is not oxidized and the dielectric layer is not reduced.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the ceramic laminated body which does not need to strictly control the oxygen partial pressure in a baking atmosphere can be provided.

  In the present invention, the dielectric layer of the ceramic laminate is an unfired dielectric layer containing a PZT-based dielectric material, and the PZT-based dielectric material occupies the main part of the composition of lead zirconate titanate. , Strontium divalent metal ions, and Ag, Na, K monovalent metal ions.

  As the B site, it is preferable to use a component in which the following combination of metal positive ions is used for partial substitution of Zr and Ti tetravalent positive ions at the B site of the ferroelectric perovskite ceramic.

(A) Combination of monovalent and pentavalent metal positive ions, M ^I _1/4 M ^V _3/4 (M ^I = Na, K, M ^V = Nb, Ta), (b) Divalent and pentavalent M ^II _1/3 M ^V _2/3 (M ^II = Mg, Zn, Ni, Co. M ^V = Nb, Ta), (c) Trivalent and pentavalent metal positive ions Combination, M ^III M ^V (M ^III = Fe, In, Sc, relatively heavy lanthanide element. M ^V = Nb, Ta), (d) M ^III _2/3 M ^V I _1/3 (M ^III = Fe, In, Sc, relatively heavy lanthanide element (M ^VI = W), (e) M ^II _1/2 M ^VI _1/2 (M ^II = Mg, Co, Ni. M ^VI = W),
The electrode layer of the ceramic laminate is an unfired electrode layer containing an electrode material. As the electrode material, Cu as a base metal electrode material, Cu to which an alloy glass frit is added, a copper alloy, or the like can be used. In particular, a material containing Cu is preferable as an electrode material of the ceramic laminate according to the present invention because it can be fired at a low temperature and is an inexpensive good electrical conductor.

In addition, as the firing atmosphere in the present invention, a single gas such as N ₂ , N ₂ —H ₂ , CO—CO _2, or a gas containing oxygen in plural kinds of gases can be used.

  In addition to being used as a capacitor, the ceramic laminate according to the present invention is made of a material having a piezoelectric effect as a dielectric layer, and is used as a piezoelectric element by alternately applying positive and negative voltages to the dielectric layer. Can do.

Moreover, it is preferable that the oxygen partial pressure in the said baking container is 1.013 * 10 < ^-1 > -1.013 * 10 < ^-5 > Pa.

By adjusting to the oxygen partial pressure, it is possible to obtain a firing atmosphere in which the electrode layer is hardly oxidized and the dielectric layer is hardly reduced. When the oxygen partial pressure is less than 1.013 × 10 ⁻⁵ Pa, since the amount of oxygen in the atmosphere is small, firing in a reducing atmosphere may occur, and the dielectric layer may be reduced. On the other hand, when it exceeds 1.013 × 10 ⁻¹ Pa, the electrode layer may be oxidized due to excessive oxygen.

[Example]
Embodiments of the present invention will be described below with reference to the drawings.

(Reference Example 1)
The manufacturing method of the ceramic laminated body used as the reference of this invention is demonstrated using FIGS. In manufacturing the ceramic laminate 1 in which the dielectric layer 11 and the electrode layers 12 and 13 shown in FIG. 1 are alternately laminated, the unfired dielectric layer containing the PZT-based dielectric material and the unfired electrode layer containing the electrode material are alternately used. An unsintered laminate 2 is prepared, and the unsintered laminate 2 is fired in a firing atmosphere into which a dielectric layer reduction inhibitor 21 and an electrode layer antioxidant 22 are introduced.

  This will be described in detail below. In this example, as shown in FIGS. 1 and 2, a ceramic laminated body which functions as a laminated piezoelectric element having a side electrode 14 and lead wires 141 and 142 on the side faces 101 and 102 and having a dielectric layer 11 having a rectangular cross section. 1. In FIG. 1, the electrode layers 12 and 13 are omitted as appropriate. The dielectric layer 11 is made of a piezoelectric material, and two electrode layers 12 and 13 adjacent to the dielectric layer 11 apply a voltage to the dielectric layer 11 to expand and contract the ceramic laminate 1 in the laminating direction. The electrode layers 12 and 13 are energized by the side electrode 14 and the lead wires 141 and 142, and the lead wires 141 and 142 are connected to a power source (not shown).

  As shown in FIG. 2, the ceramic laminate 1 has the dielectric layer 11 having the electrode layer 12 exposed on the side surface 101, the electrode non-formed portion 120 on the opposite side surface 102, and the electrode non-formed portion 130 on the side surface 101. Then, the dielectric layers 11 from which the electrode layers 13 are exposed are alternately laminated on the opposite side surface 102. A side electrode 14 is provided so as to cover the end surface of the electrode layer 12 exposed on the side surface 101, and a lead wire 141 is provided on the side electrode 14. Similarly, the side electrode 14 and the lead wire 142 are provided on the side surface 102.

  Next, the detail of the manufacturing method of the ceramic laminated body 1 is demonstrated. Raw material powder containing a PZT-based dielectric material that can be fired at 950 ° C. is mixed with a ball mill, calcined at 700 to 850 ° C. for 5 hours, and then pulverized with a pearl mill. The obtained pulverized powder is mixed with a low melting point additive so that it can be fired at 950 ° C., and a resin and an organic solvent are added to form a slurry. A green sheet is obtained from the obtained slurry by a doctor blade method, and this green sheet is used as an unfired dielectric layer.

A predetermined amount of Cu, CuO, CuO ₂ (these copper and copper compounds are used as electrode materials) were mixed in a predetermined amount, and a powder having the same composition as that of the dielectric layer was made into a paste. The electrode paste is screen printed on the unfired dielectric layer 2 in a predetermined pattern to form an unfired electrode layer.

  20 sheets of the unfired dielectric layer thus provided with the unfired electrode layer were laminated and pressure-bonded. Subsequently, it cut | disconnected so that the surface of a lamination direction and a perpendicular direction might become a predetermined | prescribed magnitude | size. As a result, a 20-layer green chip was obtained. Subsequently, another 20 layers of the green chips were stacked and the chips were pressure-bonded to form an unfired laminate 2.

Subsequently, the binder containing CuO and Cu ₂ O was subjected to a binder removal treatment in the unfired laminated body 2 at a temperature of 500 ° C. for 5 hours. Thereafter, electrode reduction baking was performed on the green laminate 2 at a temperature of 330 ° C. for 12 hours. Furthermore, since the electrode is oxidized, electrode reduction is performed using H ₂ in the vicinity of 300 ° C. For those not containing CuO and Cu ₂ O, the binder removal treatment is performed in a nitrogen atmosphere, and the electrode reduction step is omitted.

  Next, the dielectric layer reduction inhibitor 21 and the electrode layer antioxidant 22 were introduced into the firing atmosphere, and firing was performed at 950 ° C. × 2 hours. The situation at the time of firing will be described with reference to FIG. As shown in FIG. 4, a beak 31 is placed in a firing furnace (not shown), and a magnesia plate 32 is placed in the beak 31 as shown in FIG. Another small and thin magnesia plate 33 is placed on the magnesia plate 32, and the unfired laminate 2 is placed thereon. Further, a plurality of thin magnesia plates 34 having a porosity of 20% are laminated on the green laminate 2. Further, as shown in the figure, a cylindrical dielectric layer reduction inhibitor 21 and an electrode layer antioxidant 22 are arranged next to the unfired laminate 2. The dielectric layer reduction inhibitor 21 is made of PZT, and the electrode layer antioxidant 22 is made of Cu.

The lid is closed on the edge 31 shown in FIG. A gas composed of CO ₂ , CO, O ₂ or the like is introduced as an atmospheric gas into the firing furnace. At the time of firing, the PZT of the dielectric layer reduction inhibitor 21 is altered by, for example, producing metallic lead while releasing oxygen into the scab 31. This reaction continues until the oxygen partial pressure in the raft 31 reaches a predetermined value. Further, Cu in the electrode layer antioxidant 22 is oxidized while absorbing oxygen in the beak 31. As a result, this reaction continues until the oxygen partial pressure in the scab 31 reaches a predetermined value.

  Accordingly, the oxygen partial pressure is naturally controlled by firing in the scab 31 and reaches the oxygen partial pressure in a state where neither the dielectric layer reduction inhibitor 21 nor the electrode layer antioxidant 22 is reduced or oxidized any more. And the beak 31 and the lid are not in close contact with each other, and gas is exchanged between the beak 31 and the firing furnace through the gap between the two. However, since the gap is not so large, the oxygen partial pressure in the kerchief 31 does not coincide with the oxygen partial pressure in the firing furnace, and as described above, a self-generated atmosphere is obtained. Therefore, the unsintered laminate 2 is less likely to cause oxidation of the unsintered electrode layer and reduction of the unsintered dielectric layer. In this way, the firing of the unfired laminate 2 is finished, and the ceramic laminate 1 is obtained. Thereafter, the side electrode 14 is joined to the ceramic laminate 1, and the lead wires 141 and 142 are joined to function as a piezoelectric element.

  Next, the function and effect of this example will be described. In firing the unfired laminate 2 of this example, the firing atmosphere must be controlled to an oxygen partial pressure that does not reduce PZT or the like of the dielectric layer and does not oxidize Cu or the like of the electrode layer. This oxygen partial pressure is a predetermined range derived from the Ellingham chart shown in FIG. 3 (the area shown by shading in the figure).

  In this example, a dielectric layer reduction inhibitor 21 made of PZT and an electrode layer antioxidant 22 made of Cu were introduced into the beak 31 together with the unfired laminate 2. That is, there is a possibility that the oxidation of the electrode layer may proceed in a firing atmosphere with a high oxygen partial pressure, but the electrode layer antioxidant 22 is a substance that is more easily oxidized than the electrode layer, and acquires oxygen in the atmosphere to itself. Is oxidized. With this reaction, the oxygen partial pressure in the firing atmosphere decreases, and the oxygen partial pressure decreases to a state in which the electrode layer is not easily oxidized.

  Also, in a firing atmosphere with a low oxygen partial pressure, the reduction of the dielectric layer may proceed in the same manner. However, the dielectric layer reduction inhibitor 21 is a substance that is more easily reduced than the dielectric layer, and is reduced before the dielectric layer. , Release oxygen into the firing atmosphere. Along with this reaction, the oxygen partial pressure in the firing atmosphere rises, and the oxygen partial pressure rises to a state where the dielectric layer is not easily reduced.

  As described above, according to this example, since the firing atmosphere naturally reaches an appropriate oxygen partial pressure, neither the oxidation of the electrode layer nor the reduction of the dielectric layer is likely to occur.

  In this example, both the dielectric layer reduction inhibitor 21 and the electrode layer antioxidant 22 are introduced into the beak 31. However, if the atmospheric gas introduced into the firing furnace is reducible, the dielectric layer reduction inhibitor. Even if only 21 is introduced, the same effect as this example can be obtained. If the gas to be introduced is oxidizing, only the electrode layer antioxidant 22 is required.

(Reference Example 2)
In this example, as shown in FIG. 5, the four surfaces of the unfired laminate 2 are covered with magnesia plates 351, 352, and 34 made of MgO, which hardly react with the unfired laminate 2, and firing is performed. By covering with the magnesia plates 351, 352, 34, gas tends to stay around the unfired laminate 2. Therefore, an atmosphere having a predetermined oxygen partial pressure generated as a result of reduction or oxidation of the unfired dielectric layer or the unfired electrode layer exposed on the surface of the unfired laminate 2 is maintained while the firing is continued. .

  Therefore, as a result, a self-generated atmosphere is formed around the unfired laminate as in the scab of Reference Example 1, the dielectric layer is hardly reduced, the electrode layer is hardly oxidized, and a good ceramic laminate is obtained. Can do. Other details are the same as those in Reference Example 1, and have the same effects as Reference Example 1.

  In the same firing as in this example, the unfired laminate may be covered with magnesia powder instead of the magnesia plate. Also in this case, the gas around the unsintered laminate stays, and the unsintered dielectric layer and the unsintered electrode layer exposed on the surface of the unsintered laminate 2 have a predetermined oxygen partial pressure generated as a result of reduction or oxidation. The atmosphere is maintained for the duration of the firing. Therefore, as a result, as in the scab of Reference Example 1, it is formed around the unfired laminated body, the dielectric layer is hardly reduced, the electrode layer is hardly oxidized, and a good ceramic laminated body can be obtained.

Further, it can be baked coated with PZT, PbZrO _3, or powder of one or more of PbTiO ₃ in place of the magnesia. In this case, oxygen is released to the surroundings when the powder is reduced. In the vicinity of the unfired laminate covered with such a powder, an oxygen partial pressure atmosphere is formed in which the electrode layer is not oxidized and the dielectric layer is not reduced. Therefore, as a result, an atmosphere similar to that in the scab of Reference Example 1 is formed around the unfired laminated body, the dielectric layer is hardly reduced, the electrode layer is hardly oxidized, and a good ceramic laminated body can be obtained. it can.

(Reference Example 3)
In this example, as shown in FIG. 6, a method of firing the unfired laminate 2 in a firing atmosphere in which an atmospheric gas passed through a dielectric layer reduction inhibitor and an electrode layer antioxidant is introduced will be described.

  This will be described in detail below. FIG. 6 illustrates firing according to this example. An atmosphere gas inlet 41, a first holding part 42 for arranging the electrode layer antioxidant 22 made of Cu powder, and a second holding part 43 for arranging the dielectric layer anti-oxidation agent 21 are provided. Atmospheric gas is introduced into the raft 31 using the atmospheric gas passage 4 having an inlet 44 to the rachi 31. The edge 31 is closed with a lid 310. The beak 31 is made of magnesium which does not easily react with the unfired laminate 2. The first holding part 42 and the second holding part 43 are preferably set to the same temperature in the beak 31.

  In the same manner as in Reference Example 1, an unfired laminate 2 having the same composition is prepared. The unfired laminated body 2 is put in the edge 31 and the lid 310 is closed. The beak 31 is installed in a firing furnace (not shown) and the atmosphere gas is introduced into the beak 31 using the atmosphere gas passage 4. The gap between the edge 31 and the lid 310 is not strictly closed, and some gas exchange occurs. However, gas exchange is not performed to such an extent that the atmosphere in the beak 31 greatly fluctuates. In other words, the inside of the beak 31 is a self-generated atmosphere.

  In the firing of this example, first, the temperature inside the firing furnace is raised and the unfired laminated body 2 is heated together with the edge 31. After reaching the predetermined temperature, the atmospheric gas is introduced from the atmospheric gas passage 4, and is heated in advance so that the temperature of the atmospheric gas is substantially the same as that of the unfired laminate 2. And atmospheric gas G0 is introduce | transduced from the atmospheric gas inlet 41, passes the electrode layer antioxidant 22 in the 1st holding | maintenance part 42, and becomes atmospheric gas G1. Thereafter, it passes through the dielectric layer reduction inhibitor 21 in the second holding part 43 and becomes atmospheric gas G2. This G2 is introduced from the inlet 44 to the raft 31.

  The state of G1 and G2 changes depending on the value of the oxygen partial pressure of the atmospheric gas G1, but excess oxygen is removed by the electrode layer antioxidant 22 regardless of whether the oxygen partial pressure of the atmospheric gas G0 is high or low. Oxygen is supplemented from the dielectric layer reduction inhibitor 21. Thus, the dielectric layer is difficult to be reduced and the electrode layer is difficult to be oxidized, and a good ceramic laminate can be obtained. Other details have the same configuration and operational effects as in the first embodiment.

Example 1
The present invention utilizes a fired container that is sealed when the green laminate is fired. That is, the unfired laminate is introduced into a firing container, and the inside of the firing container is evacuated. Thereafter, an atmospheric gas is introduced so that the inside of the firing container has a predetermined oxygen partial pressure, and the firing container is heated to fire the unfired laminate.

  In the present invention, after the inside of the firing container is once evacuated, the atmospheric gas is introduced so as to have a predetermined oxygen partial pressure, so that the oxygen partial pressure can be easily adjusted. Furthermore, because the firing atmosphere in the firing container is unlikely to cause gas exchange with the outside, the firing atmosphere around the unfired laminate is naturally due to the absorption of oxygen accompanying the oxidation of the electrode layer and the release of oxygen accompanying the reduction of the dielectric layer. The atmosphere becomes an oxygen partial pressure in which the electrode layer is not oxidized and the dielectric layer is not reduced. Thus, the dielectric layer is difficult to be reduced and the electrode layer is difficult to be oxidized, and a good ceramic laminate can be obtained. Other details have the same configuration and operational effects as in the first embodiment.

The perspective view of the ceramic laminated body in the reference example 1. FIG. The expanded view of the ceramic laminated body in the reference example 1. FIG. The diagram which shows the area | region of the temperature and oxygen partial pressure which were derived from the Ellingham chart in Reference Example 1, and Cu is not oxidized but PZT is not reduced. Explanatory drawing of baking in the reference example 1. FIG. Explanatory drawing of baking which enclosed 4 surfaces of the unbaking laminated body in the reference example 2. FIG. Explanatory drawing which introduce | transduces and bakes atmospheric gas in the unbaking laminated body in the reference Example 3. FIG.

Explanation of symbols

1. . . Ceramic laminate,
11. . . Dielectric layer,
12,13. . . Electrode layer,
2. . . Unfired laminate,
21. . . Dielectric layer reduction inhibitor,
22. . . Electrode layer antioxidant

Claims (3)

When manufacturing a ceramic laminate in which dielectric layers and electrode layers are alternately laminated, an unfired laminate in which unfired dielectric layers containing PZT-based dielectric materials and unfired electrode layers containing electrode materials are alternately laminated is prepared. The unfired laminate is introduced into a firing container, the inside of the firing container is evacuated, an atmospheric gas is introduced so as to have a predetermined oxygen partial pressure, and then firing is performed. Production method. 2. The method for manufacturing a ceramic laminate according to claim 1, wherein the dielectric layer contains an electrode material made of at least one of Cu, Cu to which a synthetic glass frit is added, and a copper alloy. 3. The method for manufacturing a ceramic laminate according to claim 1, wherein the oxygen partial pressure in the firing container is 1.013 × 10 ^{−1 to} 1.013 × 10 ⁻⁵ Pa.

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