JPH0468764B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a high dielectric constant thick film capacitor constituting a hybrid integrated circuit.

Conventionally, thick film capacitors consisting of a ceramic substrate, a lower electrode, a barium titanate dielectric layer formed on it, and an upper electrode formed on it are fired at a temperature of 900 to 1050°C. and relative dielectric constant
Methods of manufacturing thick film capacitors of the order of 800 to 1000 are known. However, this method requires a high firing temperature of 1300 to 1400°C for the barium titanate dielectric, so the barium titanate dielectric cannot be sufficiently sintered at a firing temperature of 900 to 1050°C. There was a problem that the originally high dielectric constant could not be obtained.

Therefore, an attempt was made to manufacture a thick film capacitor using a perovskite-type oxide dielectric that is sintered at the firing temperature of the prior art in the same manner as the conventional method, but this also resulted in a high The dielectric constant could not be obtained.

In this way, even if a thick film capacitor is formed using a dielectric material that can be sufficiently sintered at normal firing temperatures, the high permittivity inherent to the dielectric material cannot be obtained because the dielectric material formed from the thick film This is thought to be due to the fact that the sintered density of the body layer is lower than that of the sintered body of a normal disk-type ceramic capacitor.

In this way, when thick film capacitors are formed using the conventional manufacturing method described above, the high dielectric constant inherent to the dielectric material cannot be obtained, so the area occupied by the thick film integrated circuit increases, making the circuit smaller and more expensive. There was a problem that it could not be integrated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a high dielectric constant thick film capacitor that eliminates the problems of the prior art and allows the high dielectric constant inherent to the dielectric to be obtained.

To achieve the above objectives, the firing temperature of normal thick films is
We conducted various experiments to form thick-film capacitors using a high dielectric constant perovskite oxide containing Pb, which is sintered at 850-950℃, as a dielectric material. As a result, a lower electrode was formed on the ceramic substrate, and the above Pb
Thick film capacitors are manufactured by forming a dielectric layer made of a high dielectric constant perovskite oxide that contains a Only an extremely small relative permittivity could be obtained compared to that of the previous method. Therefore, the present inventor formed a lower electrode on a green sheet that was sintered to become a ceramic substrate, formed a dielectric layer on top of it, further formed an upper electrode on top of it, and then simultaneously fired it. However, it has been found that the shrinkage of the dielectric layer progresses at the same time as the shrinkage of the substrate due to sintering, and as a result, a sufficient sintered density can be obtained and the object of the present invention can be realized.

That is, the present invention provides compositions such that an alumina-glass composition consisting of 40 to 60% by weight of alumina and 60 to 40% by weight of crystalline glass and a lead-based high dielectric constant perovskite oxide can be fired simultaneously. After the adjustment, a lower electrode is formed on the green sheet of the alumina-glass composition, and the lead-based high dielectric constant perovskite oxide layer is formed thereon,
This method of manufacturing a high dielectric constant thick film capacitor is characterized in that an upper electrode is further formed thereon and fired at the same time.

The green sheet that serves as the substrate here is
It must not react with the dielectric material and deteriorate its properties. Preferably, a dielectric layer with a thickness of about 30 μm is formed from the same material as the dielectric under the lower electrode. In addition, the lower electrode is placed on the green sheet.
After forming the dielectric layer and the upper electrode, they are bonded using a hot press and then simultaneously fired to further increase the sintered density of the dielectric layer, resulting in a thickness that is almost close to the high dielectric constant inherent to the dielectric. A membrane capacitor is obtained.

The green sheet according to the present invention, which is sintered to become a ceramic substrate, is made of alumina and crystalline glass, and the ratio is 40 to 60% by weight of alumina and the balance is sintered at approximately the same temperature as the dielectric. becomes glass. Appropriate amounts of organic binder, organic solvent, plasticizer, etc. are added and mixed to the above alumina/glass powder, and green sheets are formed by a conventional method. Examples of organic binders include polyvinyl butyral, ethyl cellulose, nitrocellulose, methyl methacrylate, butyl methacrylate, etc.; examples of organic solvents include ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, diethylene glycol monobutyl ether,
Toluene, xylene, etc. are used, and as the plasticizer, for example, dioctyl phthalate, dibutyl phthalate, butylphthalyl butyl glycolate, etc. are used.

Further, as a thermocompression bonding device for thermocompression bonding the green sheet and the dielectric material to increase the density, for example, a heat press machine using a mold is suitable.

In addition, the dielectric material of thick film capacitors is PbO, Fe ₂ O ₃ ,
Composed of WO ₃ and Nb ₂ O ₅ . These oxides
PbO66.09% by weight (hereinafter simply expressed as %),
It is blended into a composition of 13.1% Fe ₂ O ₃ , 7.47% WO ₃ , and 13.34% Nb ₂ O ₅ , mixed, calcined, and pulverized using conventional techniques to create a dielectric fine powder of 15 μm or less. The dielectric powder thus obtained is a high dielectric constant perovskite-type oxide that is sintered at a temperature of 950° C. or lower, has a Curie point at room temperature, and has a dielectric constant of 15,000 or more at the Curie point. Next, an appropriate amount of the dielectric powder is mixed with an organic vehicle consisting of an organic binder and an organic solvent, and sufficiently dispersed using a triple roll or the like to prepare a dielectric paste having a viscosity suitable for screen printing. Examples of organic binders include ethyl cellulose, polyvinyl butyral, and nitrocellulose; organic solvents include α-terpineol, β-terpineol, butyl carbitol, ethyl carbitol,
Butyl carbitol acetate and the like are used.

Further, for the upper and lower electrodes of the thick film capacitor, a commercially available electrode paste mainly composed of Ag/Pb can be used.

The present invention will be explained in detail below using examples.

The composition of the green sheet that will be sintered to become a porcelain substrate is 45% crystalline glass powder and alumina powder.
Wet-mix 55% in an alumina ball mill and dry to obtain glass/alumina mixed fine powder (average particle size).
0.8 μm) was obtained. 100 parts by weight of the obtained glass/alumina mixed powder (hereinafter simply referred to as parts), 5.7 parts of polyvinyl butyral as an organic binder, 43 parts of ethylene glycol monomethyl ether and 7.2 parts of diethylene glycol monobutyl ether as an organic solvent, and dioctyl phthalate as a plasticizer. 1.08
After mixing with a homogenizer (high-speed mixer) for 30 minutes, the mixture was degassed under vacuum to obtain a slurry with a viscosity of 5000 centipoise. Next, this slurry was passed through a doctor blade to produce a green sheet with a thickness of 1.2 mm. on the other hand,
Oxide PbO 66.09%, Fe ₂ O ₃ 13.10%, WO ₃ 7.47
%, Nb ₂ O ₅ 13.34%, wet-mixed in a resin ball mill and dried, 750%
The mixture was calcined for 2 hours at a temperature of 15°C and wet-pulverized in a ball mill to obtain a dielectric fine powder with a powder particle size of 15 μm or less. Using a triple roll, 100 parts of this dielectric fine powder was uniformly dispersed in 20 parts of an organic vehicle prepared by dissolving 10% ethyl cellulose in α-terpineol to obtain a dielectric paste having a viscosity suitable for screen printing. Created.

The thick film capacitor is constructed by printing and drying an electrode paste on the green sheet 1 described above, which will be sintered to become a ceramic substrate, as shown in the plan view of FIG. 1 and the cross-sectional view of FIG. The electrode 2 is formed, and the dielectric paste described above is printed on it.
A dielectric layer 3 was formed by drying, and an electrode paste was printed and dried on top of the dielectric layer 3 to form an upper electrode 4, followed by firing in a belt furnace. The firing temperature was 850 to 950°C for 10 minutes each to investigate the effect of the sintered density of the dielectric layer on the dielectric constant of the thick film capacitor, and thick film capacitors with different sintered densities were manufactured. The capacitance of the obtained thick film capacitor is 25
Measurements were made at a frequency of 1KHz using an LCR meter in an air-conditioned room at ℃, and the relative dielectric constant was calculated using the following formula.

ε=Cd/0.0885S where C is the capacitance (pF), S is the electrode area (cm ² ), and d is the dielectric thickness (cm).

FIG. 3 shows the measurement results of the thick film capacitor obtained according to the present invention, showing the relationship between the sintered density and the dielectric constant. As is clear from the curve in FIG. 3, it can be seen that the relative dielectric constant increases as the sintered density of the dielectric layer increases. The sintered density of the dielectric layer of the thick film capacitor formed on the green sheet which is sintered to become the ceramic substrate in this manner is comparable to that of the sintered body of a normal disk-type ceramic capacitor. Therefore, the dielectric constant exceeds 10,000, approaching the original dielectric constant of the dielectric material, and is more than 10 times that of the conventional thick film capacitor.

As described above, according to the present invention, when a thick film capacitor is formed using a high dielectric constant perovskite oxide that is sintered at a normal thick film firing temperature as a dielectric, it is sintered and attached to a ceramic substrate. By forming a lower electrode, a dielectric layer, and an upper electrode in this order on a green sheet, or by further forming the same dielectric layer between the green sheet and the lower electrode, the high dielectricity inherent to the dielectric material can be improved. thick film capacitors can be obtained. In addition, the composition of the glass and alumina of the green sheet that will be sintered to become the ceramic substrate is selected so that it is sintered at the same temperature as the firing temperature of the high dielectric constant perovskite oxide, and the lower and upper electrodes are made of Ag/Alumina. It was confirmed that a thick film capacitor with the high dielectric constant inherent to high dielectric constant perovskite oxides can be obtained by co-firing using an electrode paste containing Pt as the main component.

[Brief explanation of drawings]

FIG. 1 is a plan view of a high dielectric constant thick film capacitor obtained by the method of the present invention, and FIG.
A sectional view and FIG. 3 are diagrams showing the dependence of the dielectric constant of a high dielectric constant thick film capacitor on the sintered density of the dielectric layer. 1... Green sheet, 2... Lower electrode, 3...
...dielectric layer, 4...upper electrode.

Claims (1)

[Claims] 1 Alumina 40-60% by weight and crystalline glass 60-40%
After adjusting the compositions of the alumina/glass composition consisting of 1% by weight and the lead-based high dielectric constant perovskite oxide so that they can be fired simultaneously, a lower electrode is placed on the green sheet of the alumina/glass composition. A method for producing a high dielectric constant thick film capacitor, comprising: forming the lead-based high dielectric constant perovskite type oxide layer thereon, further forming an upper electrode thereon, and firing at the same time.