JPH0332904B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a ceramic capacitor, and particularly to a highly reliable ceramic capacitor that prevents deterioration of insulation resistance at high temperatures.

(Prior Art) In recent years, as electronic components have become smaller and lighter, ceramic capacitors have also been pursued to be smaller and lighter. In particular, with regard to ceramic capacitors, in parallel with the progress of miniaturization, studies are being conducted to increase the capacitance, and as a means of achieving this, attempts are being made to reduce the thickness of the capacitors.

The following improvements can be considered as means for making ceramic capacitors thinner.

A method of forming a thin dielectric ceramic layer using a vacuum thin film forming method such as a sputtering method, a vacuum evaporation method, an ion plating method, or a vapor phase evaporation method.

A method of making the dielectric ceramic layer as thin as possible by microcrystallizing the dielectric ceramic material.

A method of obtaining a grain boundary insulated dielectric ceramic layer by forming an insulating layer at the grain boundaries of a thin semiconductor ceramic layer.

Among the above methods, there is a method in which internal electrodes are formed between a plurality of dielectric ceramic layers to form a laminated ceramic capacitor to further increase the capacitance.

(Problems to be Solved by the Invention) However, after thinning the dielectric ceramic layer by the above method, electrodes for taking out the capacitance can be formed by sputtering, vacuum evaporation, ion plating, or vapor phase evaporation. When a ceramic capacitor is formed by a method or an electroless plating method, various troubles occur. What is particularly noticeable is the deterioration of insulation resistance when used at high temperatures.

The biggest cause of this trouble is that the dielectric ceramic is made of metal oxide, and the electrodes are made of metal. That is, according to such a combination,
At the interface where the metal oxide constituting the dielectric ceramic and the metal constituting the electrode come into contact, it is thought that exchange of oxygen occurs as an inevitable phenomenon. This exchange of oxygen is difficult to recognize at room temperature, but as the temperature rises, exchange of oxygen begins to take place.

For example, if the dielectric ceramic is TiO ₂ and the electrode is
Taking a ceramic capacitor made of Cu as an example, at high temperature, for example 150℃,
TiO ₂ and Cu change as follows.

TiO ₂ reduction TiO ₂ −x Cu oxidation CuOx (0<x<2) When oxygen exchange occurs between the dielectric ceramic and the electrode in this way, the dielectric constant (ε) of the dielectric ceramic changes. Of course, the insulation resistance (IR) changes significantly, and its value generally decreases by more than two orders of magnitude.

Such a reduction is particularly noticeable when the dielectric ceramic layer is made thinner, and applies to the ceramic capacitor obtained by the above-mentioned improvement means for making the ceramic capacitor thinner.

(Objective of the Invention) Therefore, an object of the present invention is to provide a highly reliable ceramic capacitor that does not cause changes in dielectric constant or deterioration of insulation resistance by having a structure that does not reduce the dielectric ceramic when used at high temperatures. With the goal.

(Structure of the Invention) That is, the present invention includes a nickel oxide layer as a first layer and a nickel nitride layer as a second layer between a dielectric ceramic and an external connection electrode formed on the surface of the dielectric ceramic. This is a ceramic capacitor characterized by a ceramic capacitor.

Here, examples of dielectric ceramics include high dielectric constant ceramics such as barium titanate and strontium titanate, titanium oxide, magnesium titanate, magnesium oxide-titanium oxide, silicon oxide, etc. These include temperature-compensated ceramics, such as semiconductor ceramics, and grain-boundary insulated dielectric ceramics, in which the grain boundaries of semiconductor ceramics are made into insulators.

Furthermore, for dielectric ceramics with a thickness of 50 μm or less, the effect becomes stronger when the first layer of nickel oxide and the second layer of nickel nitride are interposed between the dielectric ceramic and the external connection electrode. . In other words, the thickness of the dielectric ceramic is 50 μm.
If the dielectric ceramic is used at a high temperature, even if the dielectric ceramic is reduced by the electrode, the dielectric ceramic has a sufficient thickness, so changes in the dielectric constant and deterioration of the insulation resistance will not be noticeable. Therefore, the dielectric ceramic of the present invention having a thickness of 50 μm or less is particularly effective. However, there is no problem in applying this invention to a dielectric ceramic having a thickness exceeding 50 μm, and it is optional to interpose a nickel oxide layer and a nickel nitride layer between the dielectric ceramic and the external connection electrode. .

As a means for forming the nickel oxide layer and the nickel nitride layer, thin film forming means such as sputtering, ion plating, vacuum evaporation, vapor deposition, and electroless plating are generally used. When first forming a nickel oxide layer, the sputtering method can be carried out by using, for example, metallic nickel as a target and using a mixed gas of argon and oxygen. Further, when forming a nickel oxide layer by a vacuum evaporation method, the nickel oxide layer can be formed, for example, by heating metal nickel or metal nickel powder and evaporating it in an oxygen-containing atmosphere. Furthermore, in the case of a vapor phase deposition method or an electroless plating method, after forming a nickel layer, a nickel oxide layer can be formed by thermal oxidation. Next, when forming a nickel nitride layer, the sputtering method can be carried out by using nickel metal as a target and using a mixed gas of argon and nitrogen as the sputtering atmosphere. Further, when forming a nickel nitride layer by ion plating, it can be carried out by heating and evaporating metallic nickel in a nitrogen atmosphere. The thickness of the nickel oxide layer and the nickel nitride layer is preferably 2 μm or less. This is because the ESR increases when the thickness exceeds 2 μm.

The type of metal used for the external connection electrode is not particularly limited, and commonly used metals such as Ag, Au, Cr, Zr, V, Ni, Zn, Cu,
One or a combination of two or more of Sn, Pb-Sn, Mn, Mo, W, Ti, Pd, Al, etc. may be used, and this external connection electrode may have a multilayer structure, such as Cr-Cu, Examples include Cr-Ni-Ag.

Examples of the structure of the ceramic capacitor according to the present invention include a ceramic capacitor made of a single layer of dielectric ceramic, and a multilayer ceramic capacitor. The present invention is also applicable to the case where the various ceramic capacitors described above are of the grain boundary insulation type.

(Example) Hereinafter, this invention will be explained in detail according to an example.

Example 1 Ceramic dielectric raw material powder having the following composition was prepared.

_Nd2Ti2O7 : 63 mol% _{, BaTiO3} : 14 mol _% ,
TiO ₂ : 23 mol% This raw material powder was mixed with polyvinyl alcohol as a binder, a surfactant, a dispersant, and water to prepare a slurry. Next, a ceramic green sheet with a thickness of 35 μm was prepared using this slurry by a doctor blade method.

This ceramic green sheet has a length of 7.0mm,
Cut into 5.0mm wide pieces and place on this sheet.
An Ag-Pd paste containing 70 wt% Ag and 30 wt% Pd was printed. Eleven ceramic green sheets with internal electrodes formed in this way were stacked so that the internal electrodes were exposed at the end faces of the stack. This laminate was fired in air at 1250°C to obtain a sintered unit.
The thickness of each dielectric layer of the obtained laminate was 20 μm.

Next, a nickel oxide layer was first formed by sputtering on the end face of this laminated sintered unit where the internal electrodes were exposed.

This nickel oxide layer was formed under the following conditions.

Sputtering atmosphere: Argon containing 10% oxygen Pressure: 2 x 10 ^-3 Torr Target: Nickel plate with a diameter of 5 inches and a thickness of 2 mm Voltage: 500VD.C. Current: 2.0A Sputtering time: 5 minutes Nickel oxide Thickness of layer: 2000 Å Subsequently, a nickel nitride layer was formed on the nickel oxide layer under the following conditions.

Sputtering atmosphere: Argon containing 10% nitrogen Pressure: 3 x 10 ^-3 Torr Target: Nickel plate with a diameter of 5 inches and a thickness of 2 mm Voltage: 470V.DC Current: 0.5A Sputtering time: 60 minutes Nickel nitride layer Film thickness: 6000 Å Then, on the nickel nitride layer, a Ni layer as a solder heat-resistant layer was formed as a first layer of external connection electrode by sputtering.

This Ni layer was formed under the following conditions.

Spatuter zero atmosphere: Argon Pressure: 2×10 ^-3 Torr Target: Nickel plate with a diameter of 5 inches and a thickness of 2 mm Voltage: 480 VD.C. Current: 2.0 A Time: 15 minutes Film thickness: 5000 Å Additionally, a Ni layer An Ag layer was formed on the second layer as an external connection electrode by sputtering.
This Ag layer serves as a solderable layer.

The Ag layer was formed under the following conditions.

Sputtering atmosphere: Argon Pressure: 2×10 ^-3 Torr Target: Ag with a diameter of 5 inches and a thickness of 5 mm
Plate voltage: 540VD.C. Current: 2.0A Time: 6 minutes Film thickness: 1 μm A high temperature accelerated load life test was conducted on the multilayer capacitor obtained through the above process under the following conditions.
In other words, this capacitor is installed in a temperature atmosphere of 150℃, and the voltage is 6 times the rated voltage (50V).
When 300V was applied and the insulation resistance (IR) was measured after 100 hours, it was 10 ¹¹ Ω. By the way, the initial value of the insulation resistance (IR) of this multilayer capacitor is 10 ¹¹ Ω.
It was hot. In addition, when installed in an atmosphere with a temperature of 45°C and a relative temperature of 95%, a rated voltage of 50V was applied, and the insulation resistance (IR) was measured after 500 hours, it was 10 ¹¹ Ω.
No change was observed compared to the initial value.

Comparative Example 1 An electrode for external connection of the first layer was prepared under the same conditions as in Example 1 without forming a nickel oxide layer and a nickel oxide layer on the laminated sintered unit obtained in Example 1.
A multilayer capacitor was fabricated by forming a Ni layer and an Ag layer serving as a second external connection electrode.

When this multilayer capacitor was tested in the same manner as in Example 1, the insulation resistance (IR) decreased to 10 ⁹ Ω after 10 hours, and deteriorated to 10 ⁶ Ω after 25 hours.

Example 2 SrTiO ₃ : 99.3 mol%, Y ₂ O ₃ : 0.3 mol%,
Each component was weighed so that the composition was 0.2 mol% of SiO ₂ and 0.2 mol% of Al ₂ O ₃ , and 10% by weight of an organic binder was added to the weighed raw materials. Mixing and grinding were performed. After granulating this, it was molded at a pressure of 1000 Kg/cm ² to obtain a disc-shaped molded product. This molded body was fired at 1350°C for 2 hours. Metal oxides such as Pb and Bi are applied to the surface of the resulting porcelain, and heat treatment is performed at a temperature of 1000 to 1200°C to convert the grain boundaries of the porcelain into insulators, creating a grain boundary-insulated semiconductor porcelain body. Created.

Using this semiconductor ceramic body, a nickel oxide layer, followed by a nickel nitride layer, and then a first layer of external connection electrodes and a second layer of external connection electrodes were formed on the surface by the same method as in Example 1. , we created a grain-boundary insulated semiconductor ceramic capacitor.

This capacitor was subjected to the high temperature accelerated load life test described in Example 1. As a result, while the initial value of insulation resistance (IR) was 10 ¹⁰ Ω,
After 100 hours, it was 10 ¹⁰ Ω, confirming that there was almost no deterioration in insulation resistance (IR).

Comparative Example 2 Using the grain-boundary insulated semiconductor ceramic body obtained in Example 2, the first test was conducted under the same conditions as in Example 1 without forming a nickel oxide layer and a nickel nitride layer on the surface of this magnetic body. A Ni layer serving as an electrode for external connection of the layer and an Ag layer serving as a second layer external connection electrode were formed to produce a grain boundary insulated semiconductor ceramic capacitor.

When this capacitor was tested in the same manner as in Example 1, the insulation resistance (IR) was
The resistance decreased to 10 ⁷ Ω, and after 25 hours, it deteriorated to 10 ⁵ Ω.

Example 3 On an alumina substrate, an Ag layer and a Ni layer were used as the lower electrode.
The layers were sequentially formed in the same manner as in Example 1, and the nickel nitride layer and nickel oxide layer were also formed in the same manner as in Example 1.

Next, a dielectric ceramic SiO ₂ film was formed on the nickel oxide layer to a thickness of 5000 Å by high-frequency sputtering.

Note that the conditions for forming the SiO ₂ film by high frequency sputtering method are as follows.

Sputtering atmosphere: Argon containing 5% oxygen Pressure: 5 × 10 ^-3 Torr Target: Quartz plate with a diameter of 5 inches and a thickness of 5 mm Input power: 500 W Time: 100 minutes SiO ₂ film thickness: 5000 Å After that, SiO 2 film thickness: 5000 Å A nickel oxide layer and a nickel nitride layer were sequentially formed on the ₂ films by the same method as in Example 1, and then a Ni layer and an Ag layer were further formed in Example 1.
A thin film capacitor made of SiO ₂ was created by sequentially forming the capacitors in the same manner as above.

The high temperature accelerated load life test described in Example 1 was conducted on this capacitor. As a result, the initial value of insulation resistance (IR) was 10 ¹³ Ω, but
After hours it was 10 ¹³ Ω.

Comparative Example 3 When creating the thin film capacitor according to Example 3, a thin film capacitor was created by carrying out the method described in Example 3 without forming the nickel oxide layer and the nickel nitride layer. .

When this capacitor was tested in the same manner as in Example 1, the insulation resistance was reduced to 10 ⁸ Ω.

(Effects) As described above, according to the present invention, by interposing the nickel oxide layer as the first layer and the nickel nitride layer as the second layer between the dielectric ceramic and the external connection electrode, the nickel oxide layer is interposed between the dielectric ceramic and the external connection electrode. It is possible to prevent the dielectric ceramic from being reduced by the electrode as seen in the above, and as a result, there is an effect that deterioration of electrical characteristics, especially insulation resistance, does not occur.

Claims (1)

[Scope of Claims] 1. A ceramic capacitor including a dielectric ceramic and an external connection electrode formed on the surface of the dielectric ceramic, wherein a first electrode is provided between the dielectric ceramic and the external connection electrode. A ceramic capacitor characterized in that a nickel oxide layer is formed as a layer and a nickel nitride layer is formed as a second layer. 2. A first external connection electrode is formed on the substrate,
A dielectric ceramic is formed on the first external connection electrode, and a second external connection electrode is formed on the dielectric ceramic. 2. The ceramic capacitor according to claim 1, wherein a nickel oxide layer is formed as the first layer and a nickel nitride layer is formed as the second layer between the connection electrode and the second external connection electrode. 3. A laminated dielectric ceramic element body consisting of a plurality of layers of dielectric ceramic and a plurality of internal electrodes arranged in a laminated state with each other via the dielectric ceramic to form a capacitance, In the multilayer ceramic capacitor in which a pair of external connection electrodes for taking out capacitance are formed, which are connected to predetermined ones of the internal electrodes, the dielectric ceramic body and the external connection electrodes are connected to each other. 2. The ceramic capacitor according to claim 1, wherein a nickel oxide layer is formed as the first layer and a nickel nitride layer is formed as the second layer. 4. The ceramic capacitor according to claims 1 to 3, wherein the dielectric ceramic has a thickness of 50 μm or less. 5 The nickel oxide layer as the first layer and the second layer.
The thickness of each nickel nitride layer is 2 μm.
A ceramic capacitor according to claims 1 to 3 below. 6. Claims 1 to 3, wherein the external connection electrode is formed by any one of a sputtering method, a vacuum evaporation method, an ion plating method, a vapor phase evaporation method, or an electroless plating method. ceramic capacitor.