JPH0666218B2 - Multilayer thin film capacitor and manufacturing method thereof - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer thin film capacitor that is small, lightweight and low cost, and a method for manufacturing the same.

2. Description of the Related Art In recent years, there has been an increasing demand for miniaturization of electronic components with the trend toward smaller and lighter equipment, higher density of electronic circuits due to the adoption of highly integrated circuits, and the spread of automatic insertion machines. . Among them, various developments have been attempted to miniaturize the capacitors as well. As is well known, the capacitance per unit volume of a capacitor is proportional to the permittivity of the dielectric and inversely proportional to the thickness of the dielectric. Therefore, in order to reduce the size of the capacitor, it is possible to achieve a large size reduction by increasing the dielectric constant of the dielectric or by reducing the thickness of the dielectric.Thus, many studies have already been conducted on thin film capacitors. The method of laminating thin films and the laminated structure of thin film capacitors are known (for example, JP-A-55-91112 and JP-A-56).
(See Japanese Patent Publication No. 144523). That is, the vacuum deposition method,
Internal electrode layers made of palladium, silver, copper, nickel, aluminum, etc. formed by a physical vapor deposition method (PVD method) such as sputtering method, and dielectrics made of aluminum oxide, silicon oxide, titanium oxide, strontium titanate, etc. A thin film capacitor in which body layers are alternately laminated is generally known.

As described above, in the conventional thin film capacitor, the internal electrode layer and the dielectric layer are formed on the smooth insulating substrate having a small surface roughness by using the physical vapor deposition method (PVD method) such as the vacuum deposition method and the sputtering method. By forming it on the top surface, it is possible to significantly reduce the film thickness, which has led to miniaturization of the capacitor. That is, in a smooth insulating substrate having a small surface roughness such as a glass substrate or a ceramic substrate subjected to a glaze treatment, the unevenness of the substrate surface is small, and therefore physical vapor deposition methods such as vacuum deposition method and sputtering method are used. The ultra-thin internal electrode layer and the dielectric layer formed by using the (PVD method) can sufficiently follow the irregularities on the substrate surface, and a uniform film thickness can be obtained for both the internal electrode layer and the dielectric layer. . This makes it possible to form the thin film laminated portion without impairing the withstand voltage characteristics required for the capacitor.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In such a conventional multilayer thin film capacitor, when a smooth insulating substrate having a small surface roughness, such as a glass substrate or a ceramic substrate on which a glaze layer is formed, is used, it becomes Has extremely low adhesion strength, which is an adverse effect on the characteristics. On the other hand, if an insulating substrate such as a ceramic substrate with a large surface roughness is used, the adhesion strength of the external electrode formed by the metal spraying method to the insulating substrate can be sufficiently obtained, but the withstand voltage characteristics required as a capacitor are deteriorated. Therefore, it is difficult to significantly reduce the thickness of the internal electrode layers and the dielectric layer, and there is a problem in that the thin film capacitor cannot be made compact, lightweight and low cost.

The present invention solves the above problems, and an object of the present invention is to provide a high quality multilayer thin film capacitor that is significantly small in size, light in weight and low in cost, and a manufacturing method thereof.

Means for solving the problem
In order to achieve the above object, the present invention provides a ceramic substrate having a glaze layer formed on at least one main surface except both ends thereof, and a dielectric layer on the glaze layer, which is laminated at each end. A pair of internal electrode layers that are alternately extended to both ends of the ceramic substrate beyond the glaze layer, and the ceramic substrate on the laminated pair of internal electrode layers and dielectric layers. Of the external electrode layer formed on both ends of the ceramic substrate, which is an extended portion of the internal electrode layer not covered by the protective film.

Action With the above configuration, the internal electrode layer and the dielectric layer are formed on the glaze layer with a small surface roughness to improve the withstand voltage characteristics, and the internal electrode layers are extended to both ends of the ceramic substrate with a relatively large surface roughness. As a result, the adhesion strength of the external electrode layer increases.

Embodiment An embodiment of the present invention will be described below with reference to FIG.

As shown in the figure, the glaze layer 2 is formed on the ceramic substrate 1.
Is formed except for both ends of the ceramic substrate 1, and a pair of internal electrode layers 3 and dielectric layers 4 are alternately laminated thereon to form a thin film capacitor, and a protective film 5 is further formed thereon.
Is formed so as to cover the surface of the thin film capacitor portion except for the portions near both ends of the non-opposing portion of the internal electrode layer 3 and the surface of the glaze-treated ceramic substrate 1 around the thin film capacitor portion, and then the protective film 5 for the internal electrode layer 3 is formed. External electrode layers 6 are formed on both ends of the ceramic substrate 1 including a portion not covered by.

As the ceramic substrate 1, it can withstand high temperatures during surface mounting,
Any inorganic material such as alumina can be used as long as it is inexpensive. The surface roughness of the ceramic substrate 1 is preferably 0.1 μm or more in average center line roughness. The surface roughness of the glaze layer 2 formed to improve the surface roughness of the ceramic substrate 1 is preferably 0.01 μm or less in average center line roughness.

Next, in order to clarify the present invention more clearly,
Comparative examples (1), (2) and (3) for comparing the characteristics with (1) and (2) will be described.

(Example (1)) On the ceramic substrate 1 made of alumina having an average center line roughness (Ra) of 0.5 μm on the surface, the glaze layer 2 (Ra: 0. 005μ
m) is formed thereon, an aluminum film having a thickness of 0.05 μm is formed as the internal electrode layer 3 by a vacuum vapor deposition method, and an aromatic polyimide thin film having a thickness of 0.4 μm is formed as a dielectric layer 4 by a vapor deposition polymerization method. After alternately stacking 15 layers, a protective film 5 made of silicon nitride was formed, and further an external electrode layer 5 made of a copper alloy having a thickness of 25 μm was formed by a low pressure plasma spraying method to obtain a laminated thin film capacitor.

(Example (2)) On the ceramic substrate 1 made of alumina whose surface has an average centerline roughness (Ra) of 1.0 μm, the glaze layer 2 (Ra: 0) having a thickness of 40 μm except for both ends of the ceramic substrate 1 is formed. .0
06 μm), a nickel film having a film thickness of 0.15 μm is formed thereon as an internal electrode layer 3 by a vacuum vapor deposition method, and an aromatic polyimide thin film having a film thickness of 0.4 μm is formed as a dielectric layer 4 by a vapor deposition polymerization method. After alternately stacking 15 layers, a protective film 5 made of silicon nitride was formed, and further an external electrode layer 6 made of a nickel alloy having a thickness of 45 μm was formed by a low pressure plasma spraying method to obtain a laminated thin film capacitor.

(Comparative Example (1)) An aluminum film having a thickness of 0.05 μm was formed as an internal electrode layer 3 by a vacuum deposition method on a ceramic substrate 1 made of alumina having an average center line roughness (Ra) of 0.5 μm on the surface. As the dielectric layer 4, 15 layers of an aromatic polyimide thin film having a thickness of 0.4 μm are alternately laminated by a vapor deposition polymerization method, then a protective film 5 made of silicon nitride is formed, and further, a 25 μm thick film is formed by a low pressure plasma spraying method. The external electrode layer 6 made of a copper alloy was formed to obtain a laminated thin film capacitor.

(Comparative Example (2)) On the ceramic substrate 1 made of alumina whose surface has an average centerline roughness (Ra) of 1.0 μm, the glaze layer 2 (Ra: 0) having a thickness of 10 μm except for both ends of the ceramic substrate 1 is formed. .0
25 μm), a nickel film having a film thickness of 0.15 μm is formed as the internal electrode layer 3 by a vacuum evaporation method, and an aromatic polyimide thin film having a film thickness of 0.4 μm is formed as a dielectric layer 4 by a vapor deposition polymerization method. After alternately stacking 15 layers, a protective film 5 made of silicon nitride was formed, and further an external electrode layer 6 made of a nickel alloy having a thickness of 45 μm was formed by a low pressure plasma spraying method to obtain a laminated thin film capacitor.

(Comparative Example (3)) A 40 μm-thick glaze layer 2 (Ra: 0.006 μm) was formed on the entire surface of a ceramic substrate 1 made of alumina having an average centerline roughness (Ra) of 1.0 μm on the surface, and then the The inner electrode layer 3 has a film thickness of 0.15 μm formed thereon by a vacuum deposition method.
As the dielectric layer 4, the nickel film of No. 3 was alternately laminated with an aromatic polyimide thin film having a thickness of 0.4 μm by a vapor deposition polymerization method, and then a protective film 5 made of silicon nitride was formed.
Further, an external electrode layer 6 made of a nickel alloy having a thickness of 45 μm was formed by a low pressure plasma spraying method to obtain a laminated thin film capacitor.

Regarding the multilayer thin film capacitors of the above Examples and Comparative Examples,
As a result of comparing the VI characteristics, spike noise due to leakage was not observed at all in the laminated thin film capacitors of Examples (1) and (2) and Comparative Example (3), and stable VI characteristics were exhibited. The withstand voltage value at this time was about 250 V / μm. On the other hand, in the multilayer thin film capacitor of Comparative Example 2, since the glaze layer 2 is thin, the ceramic substrate 1
The withstand voltage drops due to the surface roughness of the
/ Μm. Further, in the multilayer thin film capacitor of Comparative Example (1), the surface roughness of the ceramic substrate 1 is greatly affected, and spike noise due to leakage from the protrusions of the ceramic substrate 1 frequently occurs in the low voltage region. It was not possible to obtain withstand voltage characteristics.

In addition, as a result of comparing the adhesion strength of the external electrodes to the ceramic substrate 1 of the multilayer thin film capacitors of the above-mentioned Examples and Comparative Examples, it was found that the results of Examples (1) and (2) and Comparative Examples (1) and (2) In the laminated thin film capacitor, the adhesion strength of the external electrode layer formed by the low pressure plasma spraying method was 10 kgf / cm ² or more, which was good, while the comparative example in which the glaze layer 2 was formed on the entire surface of the ceramic substrate 1 ( In the multilayer thin film capacitor of 3), the adhesion strength of the external electrode layer 6 formed on the glaze layer 2 by the low pressure plasma spraying method is significantly reduced,
The minimum value is less than 1 kgf / cm ² , and peeling occurs frequently, so it does not satisfy the level required as a capacitor.

In this embodiment, the case where the glaze layer 2 is provided on one main surface of the ceramic substrate 1 has been described, but also when the glaze layers are formed on both main surfaces and the laminated thin film capacitor is formed on both main surfaces. The present invention can be applied.

EFFECTS OF THE INVENTION As is apparent from the above-described embodiments, according to the present invention, a ceramic substrate having a glaze layer formed on at least one main surface except for both ends, and a dielectric layer interposed between the ceramic substrate and the glaze layer. A pair of internal electrode layers that are laminated by alternately extending over the glaze layer at both ends of the ceramic substrate, and a pair of internal electrode layers and a dielectric layer that are laminated. Since the protective film is formed excluding both end portions of the ceramic substrate and the external electrode layers formed on both end portions of the ceramic substrate of the extended portion of the internal electrode layer not covered by the protective film, Withstand voltage,
It is possible to provide high quality multilayer thin film capacitors that are compact, lightweight and low cost.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a multilayer thin film capacitor of one embodiment of the present invention. 1 ... Ceramic substrate, 2 ... Glaze layer, 3 ... Internal electrode layer, 4 ... Dielectric layer, 5 ... Protective film, 6 ... External electrode layer.

Claims (5)

[Claims] 1. A ceramic substrate having a glaze layer formed on at least one main surface except for both ends thereof, and a ceramic substrate laminated on the glaze layer with a dielectric layer interposed therebetween, and one end of the ceramic substrate exceeds the glaze layer. A pair of internal electrode layers that are alternately extended and arranged on both ends of the ceramic substrate, and both ends of the ceramic substrate are removed on the laminated pair of internal electrode layers and dielectric layers. A multilayer thin film capacitor having a formed protective film and external electrode layers formed on both ends of the ceramic substrate in an extended portion of the internal electrode layer not covered by the protective film. 2. The average centerline roughness of the surface of the glaze layer is 0.
The multilayer thin film capacitor according to claim 1, which has a thickness of 01 μm or less. 3. The multilayer thin film capacitor according to claim 1, wherein the average centerline roughness of both ends of the ceramic substrate having no glaze layer is 0.1 μm or more. 4. A step of forming a glaze layer in a region of at least one main surface of the ceramic substrate excluding both end portions, and one end portion of the both ends of the glaze layer and the glaze layer-free ceramic substrate. Up to one internal electrode layer, a dielectric layer is formed on the internal electrode layer formed on the glaze layer, and the other of the both ends of the ceramic substrate is sandwiched across the dielectric layer. Forming the other internal electrode layer up to the end, and alternately laminating the internal electrode layer and the dielectric layer, and placing both ends of the ceramic substrate on the laminated internal electrode layer and dielectric layer. A method of manufacturing a multilayer thin film capacitor, comprising: a step of forming a protective film, and a step of forming external electrode layers on the internal electrode layers on both ends of the ceramic substrate not covered by the protective film. 5. The method of manufacturing a multilayer thin film capacitor according to claim 4, wherein the external electrode layer is formed by a low pressure plasma spraying method.