JP2017014095A - Dielectric ceramic composition and dielectric element having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dielectric ceramic composition which is free from Pb and can be burnt at low temperature and a dielectric element having the same.SOLUTION: A dielectric ceramic composition is represented by a compositional formula: 100[1-x(0.94BiNaTiO-0.06BaTiO)-xKNaNbO]+αCuO+βLiF (where, x is 0.14-0.28, and for α and β, (I) α is 0.4-1.5 and β is 0-2.4 or (II) α is 0-1.5 and β is 0.2-2.4) and has a sintering density of 93% or more.SELECTED DRAWING: None

Description

  The present invention relates to a dielectric ceramic composition and a dielectric element having the same.

  In recent years, electronic components have been used in various fields, and there are cases where they are used in harsh environments. For example, electronic components used for the operation of power devices based on SiC or GaN, which are expected as devices for automobiles, or for noise removal in the engine room of automobiles, for example, have a dielectric constant even at a high temperature of 200 to 350 ° C. The temperature characteristic of the rate is required to be good. However, since barium titanate, which is often used as a dielectric ceramic composition constituting a capacitor, has a Curie temperature near 130 ° C., the relative permittivity is greatly reduced in a temperature region of 150 ° C. or higher. There was a problem that it was not possible to satisfy the request.

Conventionally, materials containing Pb have been used for such high temperature applications. For example, a two-component dielectric ceramic component such as PbTiO ₃ —BaZrO ₃ has a temperature dependence of relative permittivity up to about 300 ° C. by utilizing the fact that the Curie point of PbTiO ₃ is around 490 ° C. It can be relatively small. In addition, Pb (Zr _0.95 Ti _0.05 ) O ₃ (PLZT) to which La is added has an antiferroelectric property different from that of the barium titanate described above, so that the bias dependence of the relative permittivity at high temperature is reduced. Can be good. These have been invented in view of the problem of barium titanate, but Pb contained in such a composition is an environmentally hazardous substance, so that it is not preferable to use it. Therefore, there is a demand for a material that does not contain Pb and has good characteristics even in a high temperature region.

  A bismuth niobic acid-based piezoelectric ceramic composition not containing lead is well known (for example, Patent Documents 1 to 3). However, these patent documents do not disclose reducing the temperature dependence of the relative permittivity in a wide temperature range for the dielectric ceramic composition. Furthermore, in the inventions such as Patent Documents 2 and 3, the firing temperature of ceramics is as high as 1050 ° C. or higher.

  When a bismuth niobate-based composition that does not contain lead and has a high Curie temperature and a good temperature characteristic is considered as the material of the dielectric layer of the multilayer capacitor, it is desirable to use a silver-palladium alloy for the internal electrode. Unlike Ni electrodes, it can be fired in an air atmosphere and the process is simple. Further, since the firing temperature is low, there is a merit in terms of cost. The silver-palladium alloy (Ag—Pd) electrode has different costs and firing temperatures depending on the ratio of silver (Ag) to palladium (Pd) (Ag / Pd), but considering the cost, the Ag ratio is preferably 7/10 or more. .

Bismuth niobic acid-based BNT-BT-KNN (Bi _1/2 Na _1/2 TiO ₃ —BaTiO ₃ —K _0.5 Na _0.5 NbO ₃ ) has been reported for co-firing with Pd electrodes. According to a study by Nagata et al. (Non-patent Document 1), it is known that reaction of Bi and Ag occurs when BKT (Bi _0.5 K _0.5 TiO ₃ ) is baked at 1050 ° C. . Thus, in an Ag—Pd electrode having a cost merit, the reaction between Bi and Ag is feared, and thus firing at a temperature of less than 1050 ° C. is desired. By doing so, electrodes of Ag / Pd = 7/3, 8/2, 9/1, etc. are also possible. In order to lower the sintering temperature, some kind of sintering aid is required. Non-Patent Document 2 reports that the dielectric constant becomes broader as the KNN ratio of BNT-BT-KNN increases. This means that the rate of change of capacitance with respect to temperature change is small. However, as the KNN ratio increases, the sintering temperature increases and the relative density of the sintered body decreases.

JP 2002-220280 A JP 2011-230962 A Japanese Patent No. 5586621

Nagata et al. , Japan Journal of Applied Physics, 52 09KD05 (2013) Dittmer et. al. , Journal of Applied Physics, 109, 034107, 2011. Journal of European Ceramics Society, 31 (2011) 2107-2117

  Increasing the KNN ratio improves the temperature characteristics of the relative permittivity, but on the other hand, there is a problem that the ceramic is difficult to burn and the sintered density is lowered. In addition, although a Pd electrode is a composition that can be realized, an Ag-Pd electrode is preferable because of its high cost, and a higher Ag content is preferable because it is cheaper (for example, Ag / Pd = 70/30). . However, when the Ag ratio is high (Ag / Pd = 90/10), it is necessary to reduce the firing temperature, which increases the technical difficulty. Further, according to Non-Patent Document 1, since Ag easily reacts with Bi, baking at less than 1050 ° C. is preferable. In view of the above, an object of the present invention is to provide a dielectric ceramic composition that does not contain Pb and can be fired at a low temperature, and a dielectric element having the same.

As a result of intensive studies by the present inventors, the present invention has been completed.
The dielectric ceramic composition of the present invention is represented by the following general formula (1).
100 [1-x (0.94Bi _1/2 Na _1/2 TiO ₃ -0.06BaTiO ₃ ) -xK _0.5 Na _0.5 NbO ₃ ] + αCuO + βLiF (1)
Here, x is 0.14 to 0.28. α and β satisfy the following condition (I) or (II). (I) α is 0.4 to 1.5 and β is 0 to 2.4. (II) α is 0 to 1.5 and β is 0.2 to 2.4. The dielectric ceramic composition of the present invention has a sintered density of 93% or more.
According to another aspect of the present invention, there is provided a laminated dielectric element having a laminate of a dielectric layer made of the above dielectric ceramic composition and an internal electrode layer made of a silver palladium alloy. Here, the silver-palladium alloy has a composition of 65 to 90 wt% silver and the balance palladium.
The laminate is preferably fired at less than 1050 ° C. In the dielectric element, the temperature change rate ΔC _{400 °} C./C _{25 ° C. of the} capacitance is 30% or less, and ΔC _peak / C _{25 ° C.} is 50% or less. The definitions of ΔC _{400 °} C./C _{25 ° C.} and ΔC _peak / C _{25 ° C.} will be described later. The time constant (RC constant) in the dielectric element is preferably 200 to 350 seconds. The definition of the RC constant will also be described later.

  According to the present invention, without using heavy metal elements such as Pb and Sb, which are environmentally hazardous substances, a low-temperature sintering of less than 1050 ° C. is possible, and a dielectric capable of co-firing with Ag / Pd = 7/3 electrodes or the like. A body porcelain composition is provided. A dielectric element having such a dielectric ceramic composition as a dielectric layer exhibits good temperature characteristics with a small change rate of relative permittivity in a wide temperature range (for example, −55 to 400 ° C.). Therefore, the dielectric element having the dielectric ceramic composition of the present invention is an in-vehicle application that is required to be used in a high temperature region, and a SiC or GaN-based wide band gap semiconductor material that is required to a higher temperature region. It is optimal as a smoothing capacitor for the power device used.

The dielectric ceramic composition of the present invention has a composition represented by the general formula (1).
x is a numerical value reflecting the ratio of BNT-BT and KNN, and is 0.14 to 0.28 in the present invention.

  α and β are numerical values that reflect the added amounts of CuO and LiF, respectively. As long as at least one of CuO and LiF is included, α is zero when CuO is not included, and β is zero when LiF is not included.

When LiF is not included (that is, β = 0), the minimum value of α is 0.4 or more. Regardless of the presence or absence of LiF, the maximum value of α is 1.5. When CuO is not included (that is, α = 0), the minimum value of β is 0.2 or more. Regardless of the presence or absence of CuO, the maximum value of β is 2.4. In summary, the following condition (I) or (II) is derived for α and β.
Condition (I) α is 0.4 to 1.5 and β is 0 to 2.4.
Condition (II) α is 0 to 1.5 and β is 0.2 to 2.4.
By making CuO and / or LiF coexist so that α and β are in the above ranges, the sintered density is improved.

  The dielectric ceramic composition of the present invention has a sintered density of 93% or more. The method for measuring the sintered density is described in the column of Examples. In order to improve the sintering density, it is usually mentioned that the sintering temperature is increased. In the dielectric ceramic composition of the present invention, for example, the above-mentioned sintering density is achieved by sintering at a sintering temperature of less than 1050 ° C. There are significant advantages to gaining.

Hereinafter, embodiments of the dielectric ceramic composition of the present invention will be described while explaining the production method. The following manufacturing method is merely an example, and is not intended to limit the manufacturing method of the dielectric ceramic composition of the present invention.
First, raw material powder containing each metal element is prepared as a starting material for producing a dielectric ceramic composition. Examples of the raw material powder include powders of oxides and carbonates of each metal element. Specifically, bismuth oxide (Bi ₂ O ₃ ), sodium carbonate (Na ₂ CO ₃ ), potassium carbonate (K ₂ CO _3). ), Barium carbonate (BaCO ₃ ), titanium oxide (TiO ₂ ), niobium oxide (Nb ₂ O ₅ ), copper oxide (CuO), and lithium fluoride (LiF) powder.

  The powder raw material is weighed so that these raw material powders match the composition of the dielectric ceramic composition (sintered body) to be finally targeted. Next, each weighed raw material powder is wet mixed by a ball mill or the like. And a calcined product is obtained by calcining the mixture obtained by wet mixing. Here, the calcination is usually performed in air. The calcination temperature is preferably 850 to 900 ° C., and the calcination time is preferably 1 to 8 hours.

The obtained calcined product is wet pulverized with a ball mill or the like and then dried to obtain a calcined powder. Next, a small amount of binder (acrylic monomer is added to the obtained calcined powder and press molded to obtain a molded body. Here, the molding pressure depends on the powder state, but it is 4 to 6 t / cm. It is preferably about ^2. The shape of the molded body is not particularly limited, and can be, for example, a disk-shaped molded body having a planar dimension φ12 mm and a thickness of about 1 mm.

  And the dielectric ceramic composition sample is obtained by baking the obtained molded object. Here, the firing is usually performed in air. The firing temperature is less than 1050 ° C., preferably 960 to 1040 ° C., and the firing time is preferably 2 to 10 hours. At this time, it is necessary to obtain a sintered density of 93% or more.

  You may form metal electrodes, such as silver, on both surfaces of the obtained dielectric ceramic composition sample. The method for forming the electrode is not particularly limited, and examples thereof include vapor deposition, baking, and electroless plating.

  The dielectric ceramic composition of the present invention may have a dielectric element as a dielectric layer, and such a dielectric element is also an embodiment of the present invention. As an example of the dielectric element of the present invention, a laminated dielectric element will be described together with its manufacturing method. This dielectric element includes a rectangular parallelepiped laminated body and a pair of terminal electrodes respectively formed on opposing end surfaces of the laminated body.

  The laminated body was provided so as to sandwich an element body in which dielectric layers and internal electrode layers (electrode layers) are alternately laminated, and to sandwich the element body from both end surfaces (vertical direction) in the lamination direction. It is composed of a pair of protective layers and the like.

  A dielectric material layer is a layer which consists of the above-mentioned dielectric ceramic composition. The thickness per layer of the dielectric layer is arbitrary, and for example, 0.1 to 100 μm can be mentioned.

  The internal electrode layers are provided so as to be parallel to each other. In the element body, the internal electrode layer is formed so that one end is exposed at one end of the laminate, and one end is exposed at the other end of the laminate. The formed ones are alternately provided in parallel.

  A silver palladium alloy is used as the material of the internal electrode layer. In the present invention, the silver-palladium alloy contains 65 to 90% by weight of silver and the balance is palladium. The high silver content is advantageous in terms of cost.

  The end portions of the internal electrode layers exposed at one end surface and the other end surface of the laminate are in contact with the terminal electrodes. Thereby, the terminal electrode is electrically connected to the internal electrode layer. The material of the terminal electrode is not particularly limited, and can be made of a conductive material mainly composed of Ag, Au, Cu or the like. The thickness of the terminal electrode is appropriately set depending on the application, the size of the multilayer dielectric element, and the like, and may be, for example, 10 to 50 μm.

Preferably, the temperature change rate ΔC _{400 °} C./C _{25 ° C.} of the capacitance at a high temperature in the dielectric element is 30% or less, and ΔC _peak / C _{25 ° C.} is 50% or less.

The temperature change rate ΔC _{400 °} C./C _{25 ° C.} is a value obtained by dividing the difference between the capacitance at 400 ° C. and the capacitance at 25 ° C. by the capacitance at 25 ° C. The temperature change rate ΔC _peak / C _{25 ° C.} is a value obtained by dividing the difference between the maximum capacitance at −55 to 400 ° C. and the capacitance at 25 ° C. by the capacitance at 25 ° C. Specifically, when the capacitance at _{400 ° C.} is C _{400 ° C.} , the capacitance at 25 ° C. (room temperature) is C _{25 ° C.} , and the maximum capacitance in the measurement range of −55 to ₄₀₀ is C _peak. From these measured capacitance values, each temperature change rate is calculated as follows.
ΔC _{400 °} C./C _{25 ° C.} = (C _{400 ° C.} −C _{25 ° C.} ) / C _{25 ° C.}
ΔC _peak / C _{25 ° C.} = (C _peak −C _{25 ° C.} ) / C _{25 ° C.}

  These electrostatic capacities are measured using the LCR meter (Hewlett Packard, 4192A or E4980A, Agilent) for the dielectric element having electrodes formed as described above. The measurement frequency is 1 kHz, and the measurement temperature range is −55 to 400 ° C.

  Preferably, the dielectric element has a time constant RC at a high temperature (for example, 150 ° C.) of 200 to 350 seconds. The time constant was evaluated at 150 ° C. The applied voltage was applied so that the electric field strength was 5 kV / mm. The capacitance was measured at 1V.

  The dielectric ceramic composition and the dielectric element of the present embodiment have been described above. However, since the dielectric ceramic composition has good DC bias characteristics when a high electric field is applied, for example, it is relatively rated. It can be suitably used for medium and high voltage capacitors having a high voltage. The present invention is not limited to the above embodiment. The dielectric element of the present invention only needs to have a laminated structure of a dielectric layer made of the above-described dielectric ceramic composition and an internal electrode layer made of silver-palladium having the above-described composition. For the method and the like, the prior art can be referred to as appropriate.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the embodiments described in these examples.

In order to produce a dielectric ceramic composition, as starting materials, bismuth oxide (Bi ₂ O ₃ ), sodium carbonate (Na ₂ CO ₃ ), potassium carbonate (K ₂ CO ₃ ), barium carbonate (BaCO ₃ ), titanium oxide Powders of (TiO ₂ ), niobium oxide (Nb ₂ O ₅ ), copper oxide (CuO), and lithium fluoride (LiF) were prepared.

  And the said powder raw material was weighed so that the dielectric ceramic composition (sintered body) after this baking might satisfy | fill said general formula (1).

  Next, each raw material powder weighed was wet mixed by a ball mill. And the calcined product was obtained by calcining the mixture obtained by wet mixing at 900 degreeC for 3 hours.

  The obtained calcined product was wet pulverized by a ball mill and then dried to obtain a calcined powder. Subsequently, a small amount of binder was added to the obtained calcined powder, and press molding was performed to obtain a disk-shaped molded body having a diameter of 12 mm and a thickness of 1 mm (Production Examples 1 to 13).

  And the dielectric ceramic composition sample was obtained by baking the obtained molded object in the following baking temperature for 3 hours in the air. The sintered density of the obtained dielectric ceramic composition sample was measured. The sintered density was measured according to JIS R 1634: 1998.

The composition, sintering temperature, and sintering density of each sample were as follows. It is required that a sintered density of 93% or higher is obtained at a sintering temperature of less than 1050 ° C. In addition, what added * to the manufacture example number means the comparative example in this invention.

x α β Sintering temperature Sintering density%
* Production Example 1 0.10 0 0 1100 ° C. 94.3
* Production Example 2 0.12 0 0 1100 ° C. 94.1
* Production Example 3 0.14 0 0 1100 ° C. 94.5
* Production Example 4 0.18 0 0 1100 ° C. 94.9
* Production Example 5 0.24 0 0 1130 ° C. 93.0
* Production Example 6 0.12 1 0 1000 ° C. 97.2
Production Example 7 0.14 1 0 1000 ° C. 96.3
Production Example 8 0.18 1 0 1000 ° C. 95.5
Production Example 9 0.24 1 0 1000 ° C. 97.3
* Production Example 10 0.12 0 1 1040 ° C. 93.0
Production Example 11 0.14 0 1 1040 ° C. 93.3
Production Example 12 0.18 0 1 1040 ° C. 93.2
Production Example 13 0.24 0 1 1040 ° C. 93.1

  Next, laminated dielectric elements having the dielectric ceramic composition of the present invention were produced (Production Examples 14 to 34). The dielectric element includes a rectangular parallelepiped laminated body and a pair of terminal electrodes respectively formed on opposing end faces of the laminated body.

  The laminated body is provided so as to sandwich an element body in which internal electrode layers (electrode layers) are alternately laminated via a dielectric layer, and sandwich the element body from both end surfaces (vertical direction) in the lamination direction. It comprised from a pair of protective layer. In the element body, dielectric layers and internal electrode layers were alternately laminated. Here, a dielectric ceramic composition satisfying the general formula (1) was used as the dielectric layer.

  The thickness of one dielectric layer was 8 μm, and 10 layers were laminated in this production example. The internal electrode layer is formed so that one end is exposed at one end of the laminate, and the other is formed so that one end is exposed at the other end of the laminate. Are alternately provided in parallel. In this production example, a silver-palladium alloy (silver is 70 wt%, the balance is palladium) was used as the material of the internal electrode layer.

  Terminal electrodes were formed so that both ends of the laminate were in contact with the exposed end portions of the internal electrode layer. Thereby, the terminal electrode and the internal electrode layer were electrically connected. In this production example, silver was used as the material of the terminal electrode. The thickness of the terminal electrode was 100 μm.

  A laminated dielectric element was manufactured so as to have the above-described design. In manufacturing, a slurry containing the calcined powder was prepared, a green sheet was prepared using the slurry, a paste containing an internal electrode raw material was separately prepared, and the paste was printed on the green sheet. The printed green sheet was laminated, pressed and cut, and fired in air for 2 hours at a predetermined sintering temperature. Thereafter, a silver paste was baked to form a terminal electrode. In this way, a dielectric element was obtained.

The firing temperature was as follows.
Production Examples 14 to 20 where α = β = 0 are 1100 ° C. Production Examples 21 to 27 in which α = 1 and β = 0 are 1000 ° C. Production Examples 28 to 34 in which α = 0 and β = 1 are 1040 ° C. By firing at these temperatures, except for Production Example 20, the dielectric layer, that is, the dielectric ceramic composition exhibited a sintered density of 93% or more. Production Example 20 did not reach a high sintered density that was worth measuring the subsequent electrical characteristics.

With respect to the obtained dielectric element, the temperature change rate and time constant of the capacitance were measured.
The composition and the temperature change rate of the capacitance of each production example were as follows. ΔC _{400 °} C./C _{25 ° C.} and ΔC _peak / C _{25 ° C.} were measured as the rate of change in capacitance with temperature. Sintering temperature is less than 1050 ° C, temperature change rate ΔC _{400 ° C} / C _{25 ° C} (hereinafter referred to as T1) is 30% or less, and ΔC _peak / C _{25 ° C} (hereinafter referred to as T2) is 50% or less. Desired. Furthermore, the time constant (RC constant, unit sec) of each production example was measured, and the following results were obtained. The R constant is preferably 200 to 350 seconds.

x α β T1 (%) T2 (%) RC
* Production Example 14 0.10 0 0 0.1 47.6 245
* Production Example 15 0.12 0 0 -3.2 40.0 220
* Production Example 16 0.14 0 0 -6.5 35.1 198
* Production Example 17 0.18 0 0 -9.2 31.3 181
* Production Example 18 0.24 0 0 -48.4 20.0 63
* Production Example 19 0.28 0 0 -20.1 17.3 52
* Production Example 20 0.30 0 0 Measurement is impossible due to low density 45
* Production Example 21 0.10 1 0 8.2 123.0 340
* Production Example 22 0.12 1 0 5.7 109.7 387
Production Example 23 0.14 1 0 -10.2 49.2 349
Production Example 24 0.18 1 0 -25.0 45.8 331
Production Example 25 0.24 1 0 -27.5 44.9 280
Production Example 26 0.28 1 0 -1.8 35.2 244
* Production Example 27 0.30 1 0 Measurement not possible due to secondary phase generation 226
* Production Example 28 0.10 0 1 9.5 119.3 390
* Production Example 29 0.12 0 1 6.2 111.9 340
Production Example 30 0.14 0 1 -15.6 10.9 304
Production Example 31 0.18 0 1 -25.2 25.2 289
Production Example 32 0.24 0 1 -28.5 42.6 243
Production Example 33 0.28 0 1 -2.3 33.9 210
* Production Example 34 0.30 0 1 Measurement not possible due to secondary phase generation 180

Claims (4)

The following composition formula 100 [1-x (0.94Bi _1/2 Na _1/2 TiO ₃ -0.06BaTiO ₃ ) -xK _0.5 Na _0.5 NbO ₃ ] + αCuO + βLiF
(Where x is 0.14 to 0.28, and for α and β, (I) α is 0.4 to 1.5 and β is 0 to 2.4, or (II) α is 0 to 1.5 and β is 0.2 to 2.4.)
A dielectric porcelain composition having a sintered density of 93% or more.   A laminate comprising a dielectric layer comprising the dielectric ceramic composition according to claim 1 and an internal electrode layer comprising a silver-palladium alloy, wherein the silver-palladium alloy has a composition of 65 to 90 wt% silver and the balance being palladium. A laminated dielectric element. A value obtained by dividing the difference between the capacitance at _{400 ° C.} and the capacitance at 25 ° C. by the capacitance at _{25 ° C.} ΔC _{400 °} C./C _{25 ° C.} , maximum value of capacitance at −55 to _{400 ° C.} and 25 ° C. The difference ΔC _peak / C _{25 ° C. obtained} by dividing the difference from the electrostatic capacity by _{25 ° C.} is that ΔC _{400 °} C./C _{25 ° C.} is 30% or less and ΔC _peak / C _{25 ° C.} is 50% or less. The dielectric element according to claim 2.   The dielectric element according to claim 3, wherein a time constant RC measured at 150 ° C, an electric field strength of 5 kV / mm, and a capacitance of 1 V is 200 to 350 sec.