JP2893704B2 - Multilayer ceramic capacitors - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention 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 an element in which a ceramic dielectric layer having a perovskite structure (for example, BaTiO ₂ ) 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 necessary, inexpensive metal materials such as Cu and Ni are oxidized and cannot be used for the internal electrode layer, leaving expensive Pd. As described above, since expensive Pd is used, the conventional multilayer ceramic capacitor is necessarily 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, 24-28 June 1986 in Milan, Italy) Holding). La ₂ NiO ₄
Is a material having a specific resistance of about 10 ⁻² Ω · cm, and a capacitor using this as an internal electrode layer and using a BaTiO ₃ layer as a ceramic dielectric layer has been studied. This capacitor is 1300
The internal electrode and the dielectric layer are co-sintered at a firing temperature of about ° C.

However, this capacitor does not have sufficient characteristics.
The tan δ (1kHz) is over 10%, which is very large and cannot be considered a practical capacitor. This is because 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 an object of the present invention to provide an inexpensive high-performance multilayer ceramic capacitor in which the bonding between an internal electrode and a dielectric layer is strong even when fired at a low tone.

Means for Solving the Problems In order to solve the problems, the inventions according to claims 1 to 3 have the following configurations, respectively.

The multilayer ceramic capacitor according to claim 1 is characterized in that the ceramic dielectric layer having a perovskite structure has (La _1-x B
a _x ) ₂ Cu _{1 + y} O ₄ 0 <x ≦ 0.30 and 0 <y ≦ 0.
Internal electrode layers made of a conductive oxide having a perovskite-like structure and having a thickness of 50 are laminated and sintered at a temperature of 850 to 1100 ° C.

In the multilayer ceramic capacitor according to a second aspect, the dielectric layer further includes BaTiO ₃ as a main component, and LiF and / or BaLiF ₃ as a sintering aid.

The multilayer ceramic capacitor according to claim 3, wherein, in addition, the dielectric layer is _{Pb (Fe 1/2 Nb 1/2) 0} · 70 (Fe 2/2 W 1/3)
_0.30 O ₃ as a main component.

The capacitor according to claims 1 to 3 is fired at a temperature of less than 1200 ° C. of 850 to 1100 ° C., but the internal electrode layer is made of (La _1-x Ba _x ) ₂ Cu _{1 + y} O ₄ . Since it is a conductive oxide represented by 0 <x ≦ 0.30, it has a sufficient sintering state while having sufficient conductivity at a firing temperature of 850 ° C. to 1100 ° C. on the other hand,
A ceramic dielectric layer having a perovskite structure also includes, for example, a dielectric layer having BaTiO ₃ as a main component and LiF and / or BaLiF ₃ as a sintering aid, or Pb.
Using _{(Fe 1/2 Nb 1/2) 0 ·} 70 (Fe 2/3 W 1/3) 0 · 30 O 3 as its primary component and the like, internal electrodes even at a low firing temperature of 850 to 1100 ° C. In a state sufficiently co-sintered with the layer.

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 small, so that the loss is small.

In addition, since the internal electrode layer contains Cu excessively in the range of 0 <y ≦ 0.5, the bonding between the internal electrode and the dielectric layer is ensured, so that the junction resistance is sufficiently low and the capacity is insufficient. And a decrease in yield due to bonding failure.

EXAMPLES Hereinafter, a multilayer ceramic capacitor according to the present invention will be described in detail with reference to the drawings illustrating 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 850-1100 ° C. As shown in FIG. 1, the first and third internal electrodes 2 are connected to the connection electrode 3 on the right side, and the second and fourth electrodes are connected to the connection electrode 3 on the left side. The capacity 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 Nb 1/2) 0 · 70} (Fe 2/3 W 1/3)
_This layer contains 0.30 O ₃ as a main component. The former is 900-1
Sintered sufficiently at a low temperature of 100 ° C. The latter is 850-10
It can be sufficiently sintered at a low temperature of 00 ° C.

The internal electrode layer 2 is represented by (La _1-x Ba _x ) ₂ CuO ₄ and 0 <x
The conductive oxide having a perovskite structure of ≦ 0.30 (preferably 0.15) contains Cu excessively in the range of 1/2 <Cu / (La _1-x Ba _x ) ≦ (1 + 0.5) / 2, (La _1-x Ba _x ) ₂ Cu _{1 + y}
It is made of a conductive oxide represented by O ₄ and having 0 <x ≦ 0.30 and 0 <y ≦ 0.50, and having a perovskite-like structure. That is, if y = 0, a perovskite structure is obtained, but since y> 0, a perovskite-like structure is obtained.

This conductive oxide has a low specific resistance value. Moreover, the excess Cu secures the bonding between the internal electrode layer 2 and the dielectric layer 1. Therefore, the resistance component R in the internal electrode layer 2 is sufficiently small. This resistance component R is one of the factors of the 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 2 made of La ₂ NiO ₄ .

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

A conductive oxide layer represented by (La _1-x Ba _x ) ₂ Cu _{1 + y} O ₄ , where 0 <x ≦ 0.30 and 0 <y ≦ 0.50, which is a perovskite-like structure, which is the internal electrode layer 2 explain.

First, a calcined powder for forming the internal electrode layer 2 is prepared. Starting materials La ₂ O ₃ , BaCO ₃ , and CuO were weighed to the required amounts, mixed in ethanol for 12 hours, dried, and then dried.
After calcining at 0 to 900 ° C., a calcined powder represented by (La _1-x Ba _x ) ₂ Cu _{1 + y} O ₄ is obtained. In this case, excess Cu may be added at the stage of the starting material, or may be added at the stage after obtaining the calcined powder. The form of addition may be copper oxide powder or metallic copper powder.

The specific resistance value ρ of the sintered body using this calcined powder was measured and evaluated by forming the powder into a directly-bonded 13 mm pellet and firing it at 1000 ° C. for 2 hours. The pressure during molding is 2t
/ cm ² , x ≦ 0.30 or less (preferably x ≦ 0.15 or less) is a low specific resistance value ρ ≦ 10 ⁻² Ω · cm. It has been confirmed by X-ray diffraction measurement that when x exceeds 0.30, it appears in a structure other than a single phase of K ₂ NiF ₄ type. In this case, the perovskite-like structure breaks down, resulting in a sintered body having high resistance.

If the amount of Cu is 50% or less (0 <y ≦ 0.50), the junction can be strengthened without adversely affecting the specific resistance value ρ even if it is excessively added. There is a tendency that the specific resistance value ρ is lower when the degree of excess is to some extent. However, if it exceeds 50%, the perovskite-like structure is destroyed, or sufficient sintering is not performed, resulting in deterioration of characteristics.

Next, this time, for 45 g of the calcined powder (x = 0.1, Cu excess amount 20%: y = 0.20) containing excess Cu obtained as described above, polyvinyl butyral 2.3 g, methanol 10 cc, 2.5 g of di-n-butylbutyl phthalate was added and mixed,
A slurry for forming an internal electrode layer was prepared. And 8mm
The above-mentioned slurry was applied to both sides of the green sheet of the ceramic dielectric layer having corners, and a device sample was prepared by forming an internal electrode layer. The sample was sintered and evaluated for device characteristics. Specifically, a green sheet having a thickness of 40 μm was obtained by a known method using BaTiO ₃ having a perovskite structure to which 1% by weight of LiF sintering aid was added.
After coating and drying, the sample was cut into 8 mm square to obtain 30 samples.

A sintered body was obtained by changing various firing temperatures, a lead wire was attached to the electrode layer, and tan δ (10 kHz) was measured.

Firing temperature… 800 ° C tanδ… 25% Firing temperature… 900 ° C tanδ… 6% Firing temperature… 1000 ° C tanδ… 4% Firing temperature… 1100 ° C tanδ… 4% Firing temperature… 1200 ° C tanδ ... 30% Is a comparative example out of the range,
Correspond to Examples. The embodiment has a sufficiently low loss. If the temperature is lower than 850 ° C., the sintering is not enough and the loss is large. If the temperature is higher than 1100 ° C., surface cracks occur during firing, and the loss increases. The capacity was 80% or more of the designed value, which was a sufficient value.

Further, when the same examination as above was conducted except that excess Cu was not included (y = 0), the loss did not decrease so much, but in many cases the capacity was less than 30% of the design value. I have.

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.

Loss was examined in the same manner as described above, except that the dielectric layer was made of BaTiO ₃ as a main component and 3 wt% of BaLiF ₃ as a sintering aid, and similar results were obtained.

The dielectric layer is _{Pb (Fe 1/2 Nb 1/2) 0} · 70 (Fe 2/3 W
_1/3) 0 _{· 30} O ₃ except that as a main component is Examination of loss in the same manner as above, the loss at the firing temperature 1000 ° C. 4
% And 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.

Effect of the Invention As described above, since the multilayer ceramic capacitor of the present invention is sintered at a low temperature, the state of the interface between the internal electrode layer and the dielectric layer is good, and the loss is low. In addition, since the connection between the internal electrode layer and the dielectric layer is ensured by the excess Cu, the loss is small, and the lowering of the yield due to the insufficient capacity due to insufficient bonding can be prevented, so that the cost is low.

[Brief description of the drawings]

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

────────────────────────────────────────────────── (5) References JP-A-63-293970 (JP, A) JP-A-63-289918 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01G 4/12

Claims (3)

(57) [Claims] 1. A ceramic dielectric layer having a perovskite structure, wherein 0 <x ≦ 0.3 represented by (La _1-x Ba _x ) ₂ Cu _{1 + y} O ₄
A multilayer ceramic capacitor in which 0 and 0 <y ≦ 0.50, and an internal electrode layer made of a conductive oxide having a perovskite-like structure is laminated and sintered at a temperature of 850 to 1100 ° C. 2. The multilayer ceramic capacitor according to claim 1, wherein the dielectric layer contains BaTiO ₂ as a main component and LiF and / or BaLiF ₂ as a sintering aid. 3. A dielectric layer _{is, Pb (Fe 1/2 Nb 1/2)} 0 · 70 (Fe
_{2/3 W 1/3) 0 · 30 O} 3 multilayer ceramic capacitor according to claim 1, wherein a main component.