JPH04357607A - Dielectric porcelain composition - Google Patents

Abstract

PURPOSE:To reduce variation in temperature of a dielectric constant by adding barium zirconate or calcium zirconate, rare earth oxide, and manganese oxide into a basic component having a specific composition incorporating barium titanate, niobium oxide and cobalt oxide. CONSTITUTION:0.15-1.90 parts by weight of a zirconium compound of either one or both of barium zirconate and calcium zirconate, 0.08-0.30 parts by weight of rare earth oxide and 0.02-0.30 parts by weight of manganese oxide are added into 100 parts by weight of a basic component expressed by a composition formula: alphaBaTiO3+betaNbO2.5+gammaCoO, wherein alpha represents 0.950-0.990; beta, 0.006-0.042; gamma, 0.002-0.020; and alpha+beta+gamma=1. Consequently, even if a dielectric layer is formed thin, variation in temperature of a dielectric constant can be reduced so that a capacitance varying ratio of a capacitor can be decreased.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric ceramic composition suitable as a dielectric for multilayer ceramic capacitors.

0002

[Prior Art and Problems to be Solved by the Invention] By making a capacitor using a dielectric ceramic composition in which bismuth oxide is added to barium titanate, it is possible to obtain a capacitor with a small change in dielectric constant due to temperature changes. What can be done is publicly known. However, the dielectric constant is 1000-2000
However, it cannot meet the demand for smaller size and larger capacity.

[0003] Furthermore, as disclosed in JP-A-61-110904, etc., a dielectric ceramic composition comprising barium titanate, cobalt oxide, niobium oxide, neodymium oxide (rare earth oxide), and manganese oxide is disclosed. is also publicly known. However, if the thickness of each dielectric layer is set to 15 μm or less, the temperature change rate of capacitance will be within the desired range (for example, ±15 μm).
%) or the dielectric loss tan δ is 2.
It becomes larger than 5%.

Therefore, an object of the present invention is to maintain a dielectric constant of 4000 or more, -5 even when the thickness of the dielectric layer is 15 μm or less.
The temperature change rate of the relative permittivity is within the range of +15% to -15% with respect to +25°C in the temperature range from 5°C to +125°C, and the dielectric loss at 25°C is 2.5% or less,
The object of the present invention is to provide a dielectric ceramic composition that can have a capacitance change rate of 3% or less after 1000 hours.

[0005] To achieve the above object, the present invention has a compositional formula αBaTiO3 +βNbO2.5 +γCoO (where α, β, and γ are 0.950≦α≦0.9900).
．． 006≦β≦0.042 0.002≦γ≦0.020 A value that satisfies α+β+γ=1) Basic component 1
00 parts by weight and a zirconium compound of either or both of barium zirconate and calcium zirconate.
．． 15 to 1.90 parts by weight and 0.08 to 0 parts by weight of rare earth oxide
．． This relates to a dielectric ceramic composition containing 30 parts by weight of manganese oxide and 0.02 to 0.30 parts by weight of manganese oxide.

[0006]

[Action] Calcium zirconate (CaZ) according to the present invention
rO3) or barium zirconate (BaZrO3)
This zirconate compound has the effect of reducing the temperature change rate of relative dielectric constant in a capacitor having a dielectric ceramic layer with a thickness of 15 μm or less. Furthermore, the zirconate compound also has the effect of reducing the capacitance change rate of the capacitor. Therefore, when a multilayer capacitor is made with the dielectric ceramic composition of the present invention, the relative permittivity is 4000 or more, and the temperature ranges from -55°C to +125°C.
Temperature change rate of capacitance in the temperature range of ℃ is within the range of -15% to +15% with respect to 25℃, dielectric loss at 25℃ is 2.5% or less, and capacitance change rate after 1000 hours is within the range of -15% to +15%. It will be less than 3%.

[0007]

[Example] In this example, a ceramic base 2 having a plurality of dielectric ceramic layers 1 shown in the drawings, a plurality of internal electrodes 3 included in this ceramic base 2, and a pair of side surfaces of the ceramic base 2 are described. A multilayer ceramic capacitor including a pair of external electrodes 4 and 5 provided on the surface is manufactured. First, in order to make 47 types of ceramic capacitors with different compositions of the ceramic substrate 2, sample No. 1 shown in Table 1 was prepared. Raw materials with 47 different compositions numbered 1 to 47 were prepared.

Table 1 shows the compositional formula αBaTiO3 of the basic components.
The values of α, β, and γ in +βNbO2.5 +γCoO are shown. Note that these α, β, and γ are BaTi
The proportions of O3, NbO2.5 and CoO are shown in molar ratios. The column of additives in Table 1 includes calcium zirconate (CaZrO3) or barium zirconate (BaZrO3), R2O3, which is added to 100 parts by weight of the basic ingredients.
Rare earth oxides and manganese oxide (Mn
The amount of O) added is shown in parts by weight.

[0009]

[Table 1]

[0010] Sample No. in Table 1. The basic components of the dielectric ceramic substrate with a composition of 1 are 0.990 (BaTiO3) + 0.008 (NbO2
．． 5) To obtain +0.002 (CoO), barium titanate (BaTiO3): 994.773 g (0
．． 990 mol parts) Niobium pentoxide (Nb2O5): 4.581g (0.990 mol parts)
0.004 mole part) Cobalt oxide (CoO): 0.646 g (0.002 mole part) was weighed. Note that these raw materials have a purity of 99.99% or more. Also, βNbO2.5 in the composition formula
Nb2O5 has been used to obtain . Nb
If 0.004 mol part of 2O5 is added, NbO2.
This is equivalent to adding 0.008 mol part of 5.

Next, 1000.00 g (100 g
Calcium zirconate (CaZrO3): 7.60g
(0.76 parts by weight) Gadolinium oxide (Gd2O3): 1.50g (0
．． 15 parts by weight) of manganese oxide (MnO): 0.50 g (0.05 parts by weight) was added to obtain a raw material mixture.

Next, an appropriate amount of water was added to this raw material mixture, wet-mixed, dehydrated, dried, and then coarsely ground to obtain a raw material powder.

Next, an organic binder, a dispersant, and
A plasticizer and a dispersion medium were added and mixed in a ball mill for 24 hours to obtain a slurry.

Next, a reverse roll coater (reverse roll coater) is used.
20 μm and 30 μm thick green sheets (
Ten green sheets were formed.

Next, palladium (Pd) paste was screened onto ten green sheets having a thickness of 15 μm to obtain the internal electrodes 3 of the multilayer capacitor 6.
printed through and then dried. Note that a Pd paste layer for obtaining 50 internal electrodes 3 was formed on each green sheet. Each Pd paste layer is 14 mm long;
It has a pattern with a width of 7 mm.

Next, ten green sheets were stacked with the side with the Pd paste layer facing up, and five green sheets each having a thickness of 30 μm without a Pd paste layer were stacked on top and bottom of this stack. , these green sheets were bonded by thermocompression. Note that the green sheet having the Pd paste layer is arranged so that the internal electrodes 3 are formed with deviations.

Next, the thermocompression bonded laminate was cut into a grid shape to obtain 50 laminate chips. Laminated chip is 9mm wide
, has dimensions of 16 mm in length.

Next, the temperature of the laminated chip was raised to 300° C. at a rate of 20° C./h in a firing furnace, and this temperature was maintained for 3 hours to burn off the organic binder. After that, it is heated to 1280℃.
The temperature was raised at a rate of 50° C./h, maintained at this temperature for 2 hours to achieve sufficient densification, and the temperature was lowered to room temperature at a rate of 150° C./h to obtain a sintered body. That is, a ceramic substrate 2 having internal electrodes 3 was obtained.

Next, a pair of external electrodes 4 and 5 shown in the drawings were formed by applying Ag paste to the paired sides of the ceramic substrate 2 and baking it at about 800° C., thereby completing the multilayer ceramic capacitor 6. . The composition (ratio of each element) of the ceramic substrate 2 of the completed multilayer ceramic capacitor 6 is substantially the same as that of the starting material.

Sample No. in Table 1 Capacitors with other ceramic compositions Nos. 2 to 47 were also sample No. It was made using the same method as capacitor 1. Note that the thickness of the green sheet on which the Pd paste layer is provided is the same as that of sample No. It was varied from 37 to 47.

Next, sample No. The relative permittivity εs, dielectric loss tan δ, rate of change in capacitance over time ΔC, and rate of change in capacitance with temperature (TC) of the multilayer capacitors according to Nos. 1 to 47 were measured. These electrical characteristics were measured in the following manner.

(1) The capacitance is measured under the conditions of relative dielectric constant εs of 25° C., frequency of 1 kHz, and voltage (effective value) of 1 volt, and this capacitance and the distance between the plurality of internal electrodes 3 (porcelain It was calculated based on the thickness of the layer 1) and the opposing area of the internal electrodes 3.

(2) Dielectric loss tan δ Measured under the same conditions as relative dielectric constant εs. In addition, this tan δ
is expressed in %.

(3) Capacitance change rate over time ΔC A capacitor sample was subjected to heat treatment at 150°C for 1 hour, and the capacitance was measured after being left at room temperature for 1 hour to determine the initial capacitance C1.
The capacitance C2 after 00 hours was measured and calculated using the following formula. △C=[(C2-C1)/C1]×100(%)

(4) Temperature characteristics of capacitance (TC) Place the sample in a constant temperature bath and measure -55, -25, 0, 25, 4
The capacitance at each temperature of 0, 60, 85, 105, and 125 degrees Celsius was measured at a frequency of 1 kHz and a voltage (effective value) of 1 volt.
Capacitance Cb at other temperatures relative to capacitance Ca at 25°C
The rate of change TC was calculated using the following formula. TC=[(Cb-Ca)/Ca]×100(%)

Table 2 shows the electrical characteristics of each sample measured by the above method, and the thickness t(
μm). In addition, in the column of temperature change rate TC of capacitance, the maximum value and minimum value within the measurement temperature range -55 to +125° C. are shown.

[0027]

[Table 2]

As is clear from Table 2, sample No. The relative dielectric constant εs of the capacitor No. 1 is 4200, tan δ is 1.90%, ΔC is 2.8%, and the temperature change rate of capacitance T
The maximum value of C is +10.4% and the minimum value is -13.3%. Note that the data for each sample in Table 2 is the average value of 50 capacitors.

In the present invention, the thickness of the dielectric per layer after firing is less than 15 μm, and the dielectric constant εs at 25° C. is 4.
000 or more, tan δ at 25°C is 2.5% or less, -5
Temperature change rate TC of capacitance in the temperature range of 5 to +125°C is in the range of -15% to +15%, capacitance change rate over time △
The goal is to obtain a multilayer ceramic capacitor with C of 3% or less. Therefore, sample no. 5-10, 16, 22,
The compositions of the multilayer ceramic capacitors Nos. 23, 29, 30, 36-39, 43, and 44 are outside the scope of the present invention.

Next, the reasons for limiting the composition of the ceramic substrate will be explained with reference to Tables 1 and 2.

Sample No. As shown in 5, α is 0.991
In this case, tan δ becomes 2.6%, and the minimum value of TC becomes −19.8%, making it impossible to obtain the target electrical characteristics. However, sample no. As shown in 1 and 4, when α is 0.990, desired electrical characteristics can be obtained. Therefore, the upper limit of α is 0.990.

Sample No. As shown in 6, α is 0.949
When εs becomes 3500, desired electrical characteristics cannot be obtained. On the other hand, sample No. As shown in 2 and 3, when α is 0.950, desired electrical characteristics can be obtained. Therefore, the lower limit of α is 0.950.

Sample No. As shown in 8, β is 0.043
In this case, εs becomes 3500 and the minimum value of TC becomes -30.4%, making it impossible to obtain the target electrical characteristics. However, sample no. As shown in 2, β is 0
．． In the case of 042, desired electrical characteristics can be obtained. Therefore, the upper limit of β is 0.042.

Sample No. As shown in 7, β is 0.005
In the case of εs is 3300, tan δ is 2.90,
The minimum value of TC is -21.2%, making it impossible to obtain desired electrical characteristics. However, sample no. As shown in FIG. 4, when β is 0.006, desired electrical characteristics can be obtained. Therefore, the lower limit of β is 0.006.

Sample No. As shown in 10, γ is 0.02
In the case of 1, εs is 3200, and desired electrical characteristics cannot be obtained. However, sample no. As shown in FIG. 3, when γ is 0.020, desired electrical characteristics can be obtained. Therefore, the upper limit of γ is 0.020.

Sample No. As shown in 9, γ is 0.001
In the case of , εs is 3100 and tan δ is 2.70%.
Therefore, desired electrical characteristics cannot be obtained. However, sample no. As shown in FIG. 1, when γ is 0.002, desired electrical characteristics can be obtained. Therefore, the lower limit of γ is 0.002.

Sample No. As is clear from 16, CaZ
When the amount of rO3 or BaZrO3 added is zero, ε
s becomes 3960, making it impossible to obtain desired electrical characteristics. However, sample no. As shown in 17, CaZ
The amount of rO3 added is 0 per 100 parts by weight of the basic ingredients.
．． At 15 parts by weight, desired electrical properties can be obtained. Therefore, the lower limit of the amount of CaZrO3 added is 0.15 parts by weight.

Sample No. As shown in 22, CaZrO3
When the amount added becomes 1.96 parts by weight, TC falls outside the desired range. However, sample no. 1.9 as shown in 21
In the case of 0 parts by weight, desired electrical characteristics can be obtained. Therefore, the upper limit of the amount of CaZrO3 added is 1.90
Parts by weight.

Note that sample No. 12-14, 23-29
As is clear from the above, BaZr instead of CaZrO3
Even if O3 is used, CaZrO3 and BaZrO
Even if CaZrO3 is used at the same time, the same effects as CaZrO3 can be obtained. That is, CaZrO3 and Ba
ZrO3 or both at a concentration of 0.15 to 1.
By adding within the range of 9 parts by weight, the capacitor targeted by the present invention can be obtained.

[0040] R2 O3 (However, R is Gd, Nd, S
The amount of rare earth oxides shown in sample No. In the case of zero as shown in 23, the minimum value of TC is -17.3 and the capacity aging rate ΔC is 4.1%, making it impossible to obtain the desired characteristics. However, sample no. As shown in No. 24, when the amount added is 0.08 parts by weight, desired electrical characteristics can be obtained. Therefore, the lower limit of the rare earth oxide is 0.08 parts by weight.

Sample No. 29, when the amount of rare earth oxide added is 0.32 parts by weight, εs is 380
0, and the desired characteristics cannot be obtained. However, sample No.
．． As shown in No. 28, when the amount of rare earth oxide added is 0.30 parts by weight, desired characteristics can be obtained. Therefore, the upper limit of the rare earth oxide is 0.30 parts by weight.

[0042] Note that the rare earth oxides include Gd2O3, N
Similar effects can be obtained using one or more of d2O3, Sm2O3, and the like.

Sample No. 37 and 43, when all additives are zero, the thickness (t) of the dielectric layer is 15
Even if it is μm, εs is less than 3820, and △C is 3
．． 12% or more, and desired characteristics cannot be obtained. Furthermore, if the thickness (t) of the dielectric layer is less than 15 μm when all additives are zero, sample No. 38, 3
As shown in Figures 9 and 44, tan δ becomes larger than 2.5% and TC goes out of range. On the other hand, when the additive according to the invention is included, sample no.
As shown in 41, 42, 46, and 47, target characteristics can be obtained even if the thickness of the dielectric layer is made smaller than 14 μm.

[0044]

[Modifications] The present invention is not limited to the above-described embodiments, but can be modified, for example, as follows. (1) The starting material for obtaining the basic component CoO is Co
Co2 O3 or Co3 O4 can be used instead of O. (2) CeO2 within a range that does not impede the purpose of the present invention
A small amount of a sintering aid such as , SiO2, etc. can be added. (3) The material of the internal electrodes 3 can be formed from Ag-Pd paste. (4) Of course, it can also be applied to single-layer capacitors.

[0045]

[Effects of the Invention] As is clear from the above, according to the present invention, in the case of an extremely thin dielectric ceramic layer, the dielectric constant is 4000 or more, tan δ is 2.5% or less, and -55°C to
Temperature change rate of capacitance at +125℃ is -15% to +15
% range, the rate of change in capacity over time ΔC is 3% or less. Therefore, a small capacitor with good characteristics can be provided.

[Brief explanation of the drawing]

The drawing is a sectional view showing the principle of a part of a multilayer ceramic capacitor according to an embodiment of the present invention.

[Explanation of symbols]

1 Porcelain layer 2 Porcelain base 3 Internal electrode 4,5 External electrode

[Table 1]

[Table 1]

[Table 1]

[Table 2]

[Table 2]

[Table 2]

Claims (1)

[Claims] Claim 1: Compositional formula αBaTiO3 +βNbO2.5 +γCoO (where α, β, and γ are 0.950≦α≦0.9900.
006≦β≦0.042 0.002≦γ≦0.020 A value that satisfies α+β+γ=1) Basic component 1
00 parts by weight and a zirconium compound of either or both of barium zirconate and calcium zirconate.
．． 15 to 1.90 parts by weight and 0.08 to 0 parts by weight of rare earth oxide
．． A dielectric ceramic composition containing 30 parts by weight of manganese oxide and 0.02 to 0.30 parts by weight of manganese oxide.