JP2893703B2 - Multilayer ceramic capacitors - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a multilayer ceramic capacitor using a conductive oxide for an internal electrode layer.

2. Description of the Related Art A multilayer ceramic capacitor having a large capacity is a device in which a ceramic dielectric layer having a perovskite structure (for example, BaTiO ₃ ) and an internal electrode layer are alternately laminated and sintered. The element is manufactured in air atmosphere, 1250
It is sintered by firing at a high temperature of 1350C. When firing at a high temperature is required, inexpensive metal materials such as Cu and Ni are oxidized and cannot be used for the internal electrode layer, and expensive Pd is used. As described above, there is a problem that the conventional multilayer ceramic capacitor using expensive Pd is inevitably expensive.

Conventionally, as a solution to this problem, the application of a conductive oxide (La ₂ NiO ₄ ) that is stable even at high temperatures has been proposed (World Congress on High-Tech Ceramics, June 24-28, 1986 in Milan, Italy) Held). La ₂ NiO
₄ is a material of resistivity of about 10- ² Ω · cm, using the internal electrode layers, the capacitor using the BaTiO ₃ has been studied in the ceramic dielectric layers. This capacitor is
The internal electrode and the dielectric layer are co-sintered at a firing temperature of about 00 ° C.

Problems to be Solved by the Invention However, this capacitor is not a practical capacitor having a very large loss tan δ (1 kHz) with insufficient characteristics. This is because the firing temperature is high and the width of the ion diffusion layer at the interface between the dielectric layer and the internal electrode layer is wide.

According to the present invention, the sintering is performed at a low temperature of less than 1200 ° C., the interface state between the internal electrode and the dielectric layer is good, and
It is another object of the present invention to provide an inexpensive high-performance multilayer ceramic capacitor in which the bonding between the internal electrode and the dielectric layer is strong even when fired at a low temperature.

Means for Solving the Problems In order to solve the problems, the inventions according to claims 1 to 5 have the following configurations, respectively.

The multilayer ceramic capacitor according to claim 1, wherein the ceramic dielectric layer having a perovskite structure has La _2-x M _x CuO
_{4 An} internal electrode layer containing Ag and a conductive oxide represented by 0 (x: 0.7, represented by M; Ba or Sr) is laminated, and 900 to 1
A multilayer ceramic capacitor sintered at a temperature of 100 ° C, where Cu is required to satisfy La _2-x M _x CuO ₄ more than 50
% In excess.

In the multilayer ceramic capacitor according to the second aspect, the content of Ag is 5 wt% or less based on 100 wt% of the conductive oxide.

The multilayer ceramic capacitor according to claim 3, wherein the content of Ag is more than 5 wt% and 80 wt% with respect to 100 wt% of the conductive oxide.
It is as follows.

In the multilayer ceramic capacitor according to the fourth aspect, the dielectric layer is mainly composed of BaTiO ₃ , and is composed of LiF and / or BaLiF _3.
As a sintering aid.

The multilayer ceramic capacitor according to claim 5, the dielectric layer _{is, Pb (Fe 1 / 2~2 /} 3 Nb 1 / 2~1 / 3) O 3 -Pb (Fe
_2/3 W _1/3 ) O ₃ as a main component.

The capacitor described in claim 1 is 900 to 1
Although it is sintered at a low temperature of less than 1200 ° C. of 100 ° C., a conductive oxide and Ag in which the internal electrode layer is represented by La _2−x MxCuO ₄ (M; Ba or Sr) and 0 <x <0.7 Since it is a layer containing, the layer is in a sufficiently co-sintered state with sufficient conductivity. In general, La _2-x MxCuO ₄ based conductive oxides easily sinter in the air with BaTiO ₃ or Pb (Fe _2/3 Nb _1/2 ) O ₃ based ceramic dielectrics with perovskite structure. However, because of the small amount of additives for improving properties contained in the dielectric material, it was practically impossible to set conditions for obtaining strong co-sintering. However, as in the present invention, when Ag is contained, if the content is 5 wt% or less with respect to 100 wt% of the conductive oxide, it enters the crystal lattice of the conductive oxide, and 5 wt% to 80 wt%. In such a case, although Ag also exists between the crystal lattices (grain boundaries), the Ag easily causes a reliable co-sintering state.

As described above, since the sintering is performed at a low temperature, the width of the diffusion layer at the interface between the dielectric layer and the internal electrode layer is narrow, and the loss (tan δ) is suppressed to a low level.

The specific resistance of the internal electrode layer is also lower than 10 ⁻² Ω · cm, which is far lower than the specific resistance of La ₂ NiO ₄ , which also contributes to low loss. A low specific resistance is also advantageous in reducing the thickness of the internal electrode layer.

In addition, Cu is 50% more than required to meet La _2-x M _x CuO ₄
Although the configuration that is excessively included in the following range is also adopted, this is by giving excess Cu, while further strengthening the co-sintering property between the internal electrode layer and the dielectric layer, By suppressing the excess amount to 50% or less, it is possible to prevent an increase in the specific resistance value due to oxidation of Cu, and as a result, to sinter at a lower temperature more reliably while eliminating an adverse effect on the specific resistance value. To realize a low-loss capacitor.

EXAMPLES Hereinafter, a multilayer ceramic capacitor according to the present invention will be described in detail with reference to the drawings showing an example thereof.

The figure shows an embodiment of the capacitor according to the present invention.

The multilayer ceramic capacitor includes a laminate in which dielectric layers 1 and internal electrode layers 2 are alternately laminated and both layers are co-sintered, and includes connection electrodes 3 and 3 provided on side surfaces of the laminate. ing. Of course, sintering is done at temperatures as low as 900-1100 ° C. As shown in the figure, the first and third inner electrodes 2 are connected to the right connection electrode 3, and the second and fourth are connected to the left connection electrode 3, respectively. The structure is such that a capacitance is provided between the matching internal electrodes 2.

The dielectric layer 1 is a ceramic dielectric layer having a perovskite structure. For example, the dielectric layer is a layer containing BaTiO ₃ as a main component and LiF and / or BaLiF ₃ as a sintering aid, or Pb (Fe _{1 / 2~2 / 3 Nb 1 /} 2~1 / 3) O 3) O 3 -Pb
(Fe _2/3 W _1/3 ) O ₃ is a layer mainly composed of O ₃ .

The internal electrode layer 2 is made of La _2-x MxCuO ₄ (however, M; Ba or Sr)
, Containing Ag and a conductive oxide satisfying 0 <x <0.7, the internal electrode layer 2 itself has a low specific resistance, and a strong co-sintering state is created between the internal electrode layer 2 and the dielectric layer 1. As a result, the junction resistance is sufficiently low.

That is, in the multilayer ceramic capacitor of the present invention,
The resistance component R in the internal electrode layer 2 is sufficiently small. This resistance component R is one of the factors of the (high-frequency) loss tan δ of the multilayer ceramic capacitor. The loss has a relationship of tan δ = ωCR, where the resistance component R, the capacitance C, and the frequency ω. Therefore, the multilayer ceramic capacitor of the present invention having a small R has a small loss. For example,
If the thickness is the same, the loss is considerably smaller than that of the conventional internal electrode layer made of La ₂ NiO ₄ .

Of course, since the dielectric layer 1 and the internal electrode layer 2 are sintered at a low temperature, the reason for this is that the loss characteristics are also low as described above.

Next, the multilayer ceramic capacitor will be described in more detail.

The specific resistance value of the internal electrode layer 2, that is, a layer containing Ag and a conductive oxide represented by La _2-x MxCuO ₄ (where M; Ba or Sr), where 0 <x <0.7, will be described.

First, a calcined powder for forming the internal electrode layer 2 is prepared.
Starting materials La ₂ O ₃ , BaCO ₃ , and SrCO ₃ CuO are each weighed in an amount required in the following cases, mixed in ethanol for 12 hours, dried, and then dried at 800 to 1000 ° C. for 2 to 2 hours. Calcination was performed for about 10 hours, and pulverization was repeated several times to obtain a calcined material for a conductive oxide.

Ag may be added at the stage of the starting material, or may be added at the stage after obtaining the calcined product. Ag addition may be in the form of AgO powder or metallic Ag powder.
Here, it is added in the form of AgO at the stage after obtaining the calcined product.

Further, Cu may be added in excess (but not more than 50%) of the amount that stoichiometrically satisfies La _2-x MxCuO ₄ . In this case, excess Cu may be added at the stage of the starting material,
You may add at the stage after obtaining a calcined material. Cu addition may be in the form of copper oxide powder or metallic copper powder. Here, it is added in the form of CuO at the stage after obtaining the calcined product.

A sintered body was prepared using the calcined powder, and the specific resistance value ρ was measured and evaluated. The sintered body was obtained by forming the powder into a pellet having a diameter of 13 mm and firing at 1000 ° C. for 2 hours in the air.
The pressure during molding is 2 t / cm ² .

_{La 1 · 9 Ba 0 · 1} CuO 4 + AgO 2wt% ^{resistivity: 3~5 × 10 -3 Ω · cm} La 1 · 7 Sr 0 · 3 CuO 4 + AgO 5wt% resistivity: 3 to 5 × 10 ^{- _{3 Ω · cm La 1 · 9}} Ba 0 · 1 CuO 4 + AgO 2wt% + CuO 2wt% ^{resistivity: 3~5 × 10 -3 Ω · cm} La 1 · 9 Ba 0 · 1 CuO 4 + AgO 30wt% resistivity : 2 ～ 3 × 10 ^-3 Ωcm For comparison, a sintered body without Ag was prepared and the specific resistance was measured.

_{La 1 · 9 Ba 0 · 1} CuO 4 ^{resistivity: 6~8 × 10 -3 Ω · cm} La 1 · 7 Sr 0 · 3 CuO 4 resistivity: a 6~8 × 10 ^-3 Ω · cm Ag In the case of including, it is clearly understood that the specific resistance value is extremely low. That is, in the ceramic capacitor of the present invention, the specific resistance of the internal electrode layer 2 itself is very low.

However, if Ag is contained in excess of 80% by weight with respect to 100% by weight of conductive oxide, the co-sintered state tends to weaken, or a large amount of expensive Ag is included. Therefore, the cost tends to increase.

Subsequently, 14.5 g of methanol, 2.3 g of polyvinyl butyral (PVB) and 2.5 g of di-n-butyl phthalate were added to and mixed with 45 g of the calcined powder for a conductive oxide, and a slurry for forming an internal electrode layer was formed. Produced. Then, the above-mentioned slurry was applied to both surfaces of the green sheet piece for the ceramic dielectric layer to form an element basic configuration sample in which an internal electrode layer was formed,
This was sintered and the element characteristics and the like were evaluated. Specifically, 1w
Using BaTiO ₃ having a perovskite structure to which LiF for sintering aid of t% was added, a green sheet having a thickness of 40 μm was obtained by a known method, and the slurry was applied to the green sheet having a thickness of 40 μm and dried. Divided into 1000 on a platinum boat
C. for 2 hours for sintering. Then, a lead wire was attached to the surface electrode layer, and the electrode resistance and tanδ (1 kHz
z) was measured.

(1) When calcined material is used Electrode resistance value 3-5 × 10 ^-2 Ω · cm tanδ 10-20% (2) When calcined material is used Electrode resistance value 3-5 × 10 ^-2 Ω · cm tanδ 10-20% (3) When calcined material is used Electrode resistance value 5-8 × 10 ^-3 Ω · cm tanδ 5-10% (4) When calcined material is used Electrode resistance value 5-8 × 10 ^-3 Ω · cm tan δ 5 to 10% For comparison, the electrode resistance and loss when using the calcined material were also measured.

(5) When calcined material is used Electrode resistance value 7-8 × 10 ^-3 Ω · cm tan δ 25-30% (6) When calcined material is used Electrode resistance value 6-7 × 10 ^-3 Ω · cm tan δ 20% to 25% As can be seen from the results, those equivalent to the examples have sufficiently low electrode resistance and loss and improved performance.

Although the actual multilayer ceramic capacitor has more dielectric layers and internal electrode layers, the evaluation is sufficient for the basic constituent elements. As the number of layers increases, the capacitance C increases and the resistance component R decreases.

The dielectric layer _{is, Pb (Fe 1/2 Nb 1/2)} 0 · 70 (Fe 2/3
W _1/3) where 0 _{· 30} O ₃ except that as a main component is examining the electrode resistance value and loss in the same manner as described above, similar results were obtained.

The present invention is not limited to the above embodiment. For example, the ceramic dielectric layer having a perovskite structure may be a layer made of a material other than those described above.

Effects of the Invention As described above, the multilayer ceramic capacitor of the present invention is sintered at a low temperature of 900 to 1100 ° C,
Moreover, since the internal electrode layer is securely bonded to the dielectric layer and the internal electrode layer itself has a low resistance value, the internal electrode layer has very low loss. In addition, when the internal electrode layer is securely bonded to the dielectric layer, a decrease in yield due to insufficient capacity or poor bonding is eliminated, and the cost is reduced.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a multilayer ceramic capacitor according to one embodiment of the present invention. 1 ... dielectric layer, 2 ... internal electrode layer, 3 ... connection electrode.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Mutsuaki Murakami 3-10-1, Higashi-Mita, Tama-ku, Kawasaki-shi, Kanagawa Matsushita Giken Co., Ltd. (56) References JP-A-63-293910 (JP, A) 63-289918 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01G 4/12

Claims (5)

(57) [Claims] 1. A ceramic dielectric layer having a perovskite structure containing a conductive oxide represented by La _2-x M _x CuO ₄ (M; Ba or Sr), where 0 <x <0.7, and Ag This is a multilayer ceramic capacitor in which electrode layers are laminated and sintered at a temperature of 900 to 1100 ° C. Cu is contained in excess of 50% or less than the required amount to satisfy La _2-x M _x CuO _4. Are multilayer ceramic capacitors. 2. The multilayer ceramic capacitor according to claim 1, wherein the content of Ag is 5 wt% or less based on 100 wt% of the conductive oxide. 3. The multilayer ceramic capacitor according to claim 1, wherein the content of Ag is more than 5 wt% and not more than 80 wt% based on 100 wt% of the conductive oxide. 4. A dielectric layer comprising BaTiO ₃ as a main component and LiF and / or BaLiF ₂ as a sintering aid.
The multilayer ceramic capacitor according to any one of the above. 5. The method according to claim 1, wherein the dielectric layer is made of Pb (Fe _{1/2 to 2/3} Nb _{1/2 to 2/3} O ₃
-Pb (Fe _2/2 W _1/3) multilayer ceramic capacitor according to any one of the O ₃ from claim 1 as a main component to 3.