JP2976625B2 - Multilayer ceramic capacitors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer ceramic capacitor used for electronic equipment and the like, and more particularly to a small-sized and large-capacity multilayer ceramic capacitor excellent in temperature stability.

[0002]

2. Description of the Related Art In recent years, a multilayer ceramic capacitor having a structure in which dielectric layers and metal conductors are alternately laminated is capable of achieving a small size and a large capacity. I have. Further, there is a strong demand for such a multilayer ceramic capacitor to be further reduced in size and capacity.

A conventional multilayer ceramic capacitor will be described below. FIG. 7 is a sectional view showing a sectional structure of a conventional multilayer ceramic capacitor. In FIG. 7, reference numeral 1 denotes a metal conductor, and 2 denotes a dielectric layer made of ceramic. The metal conductor 1 is laminated so as to face the dielectric layer 2. Reference numeral 3 denotes terminal electrodes formed at both ends of the laminate so as to be connected to the metal conductor 1.

In the conventional multilayer ceramic capacitor configured as described above, efforts have been made in the past to increase the dielectric constant of the dielectric and reduce the thickness of the dielectric layer 2 in order to obtain a large capacitance. .

On the other hand, a ceramic dielectric having a high dielectric constant used for a multilayer ceramic capacitor has a strong temperature dependence as shown in the dielectric constant-temperature characteristics shown in FIG. 8, and has a maximum point near the phase transition temperature Tc.

Accordingly, in order for the multilayer ceramic capacitor to exhibit a sufficiently high capacitance in the operating temperature range, it is necessary to increase the dielectric constant of the ceramic dielectric used and to weaken the temperature dependence of the dielectric constant.

[0007] For this purpose, a method of incorporating additives called shifters or depressors into a ceramic dielectric has been generally adopted. Where the shifter is the phase transition temperature T
It is intended to be added to move the c, depressor is intended to be added to attenuate the temperature dependence of the dielectric constant.

[0008]

However, the conventional multilayer ceramic capacitor described above has a problem that a small-sized large-capacity multilayer ceramic capacitor having excellent temperature stability cannot be obtained for the following reasons.

(1) A ceramic dielectric having a high dielectric constant generally has a large rate of temperature change, and if a shifter or a depressor is added to the dielectric to improve this, the dielectric constant of the dielectric decreases or the dielectric loss decreases. Or the reproducibility in the manufacturing process decreases.

(2) Due to the thinning of the dielectric material, defects such as pinholes are likely to occur during the formation of the thin film, which lowers the yield in the manufacturing process, lowers the DC breakdown voltage, and increases the dielectric loss.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a small-sized and large-capacity multilayer ceramic capacitor having excellent temperature stability.

[0012]

Means for Solving the Problems The multilayer ceramic capacitor of the present invention to achieve this purpose, a metal conductor and a dielectric layer are laminated alternately to form a capacitor body, capacitor body of the capacitor body Nico Is provided with a heating element for controlling the temperature at a constant level.

[0013]

With the above construction, the temperature of the multilayer ceramic capacitor thermally coupled by the heating element is kept constant, so that the dielectric constant having a high dielectric constant near the phase transition temperature Tc and a large temperature change of the dielectric constant. Even if a body is used, a high dielectric constant can be obtained stably in the operating temperature range, and as a result, a small-sized and large-capacity multilayer ceramic capacitor excellent in temperature stability can be obtained.

[0014]

Embodiment (Embodiment 1) An embodiment of the present invention will be described below.

FIGS. 1 to 3 are views showing a multilayer ceramic capacitor according to an embodiment of the present invention. Here, the same parts as those shown in FIG. 7 are denoted by the same reference numerals. In FIG. 1, reference numeral 1 denotes a metal conductor, and a capacitor body is formed by laminating a desired number of layers so as to alternately face each other with a dielectric layer 2 made of ceramic therebetween. Terminal electrodes 3 connected to the metal conductor 1 are provided at both ends of the capacitor body.

Reference numeral 4 denotes a buffer layer provided on the uppermost layer of the capacitor body together with a support layer which does not contribute to the capacitance. heating element comprising a body 6 heating element metal conductor 7 for are provided. Reference numeral 8 denotes a glass protective layer covering the heating element, and 9 denotes a terminal electrode, which is formed on both end surfaces of the buffer layer 4 and the dielectric layer 2 , and electrically connects the metal conductor 1 and the heating element metal conductor 7. ing.

Hereinafter, a method for manufacturing the multilayer ceramic capacitor of the present invention and a comparative example will be described.

First, a dielectric material having a phase transition temperature Tc of 15 ° C./90° C. in a BaTiO ₃ —Ce _2/3 TiO ₃ system was prepared.
Prepared by conventional ceramic techniques, a butyral resin, a plasticizer, in addition to a solvent combined mixed, after preparing the slip, to produce a green sheet having a thickness of 20μm by a tape casting method.

The self-temperature control range is 90 to 95 ° C.
Then, a barium titanate-based positive temperature coefficient thermistor having a specific resistance of 250 Ωcm is prepared by a usual ceramic method , and a SiO ₂ —B ₂ O ₃ —PbO—CaO-based glass having a softening point of 500 ° C. in a weight ratio of 2: After adding ethyl cellulose and butyl carbitol, the mixture was kneaded with a three-roll mill to prepare a barium titanate-based positive temperature coefficient thermistor.
Furthermore, the softening point is 500 ° C., SiO ₂ —B ₂ O ₃ —PbO—
Ethyl cellulose and butyl carbitol are added to CaO-based glass, and then kneaded with a three-roll mill to prepare a glass paste.

Next, to the green sheet overlapping area of metallic conductors in 4.7 mm ^2, the multi-piece designed to lead portion for connection with the terminal electrodes are arranged in the longitudinal direction The metal conductor is screen-printed using a printing pattern and using a Pd paste to produce a green sheet on which the metal conductor is printed.

Next, as a support layer not involved in the capacitance , 17 green sheets, 7 green sheets on which metal conductors are printed, and a buffer layer 4 thereon, having a thickness of 7 , 10, 10 The required number of green sheets of dielectric material are stacked and pressurized so as to have a thickness of 20 μm, cut into individual pieces, and fired at 1320 ° C. After obtaining this sintered body, the end face of the sintered body is polished to secure the connection between the metal conductor 1 and the terminal electrode 3, and the terminal electrode is attached to both end faces of the polished sintered body. and then by applying a a g paste, after baking at 800 ° C., by electroplating to form a Ni and solder plating layer.

Next, as the buffer layer 5 of the heating element 6 , the thickness 7 ,
A barium titanate-based positive temperature coefficient thermistor paste is screen-printed to a thickness of 10, 20 μm.

Next, as the heating body a metallic conductor 7, the Ag paste barium titanate based PTC thermistor and ohmic contact is added ingredients such as is done, for connection to the terminal electrode in the overlapping area of 2 mm ² the screen-printed by the printing pattern that is designed to lead portion are arranged in the width direction, further the thickness of the titanium barium-based PTC thermistor paste was screen printed so as to 10μm on this, then titanium Ag added with a component that makes ohmic contact with a barium acid-based positive temperature coefficient thermistor
Screen-print the paste again.

Finally, a glass paste is screen-printed and formed as a glass protective layer 8 to manufacture a multilayer ceramic capacitor.

Further, as shown in FIG. 2, the terminal electrode 9 of the heating element 6 is provided in the width direction while the terminal electrode 3 for taking out the capacitance of the capacitor is provided in the length direction. Has been granted. At this time, the terminal electrodes 3 and 9 are formed simultaneously.

FIG. 3 shows an electric circuit diagram of the present embodiment. FIG.
In the figure, reference numeral 6 denotes a heating element, and a broken line 10 denotes a state in which the heating element is thermally coupled to the heating element of the multilayer ceramic capacitor. 11 is a power supply. In addition, by providing a buffer layer with a thickness of 10 μm or more of each material so that the heating element portion and the capacitor body are not affected by characteristic deterioration due to mutual diffusion during the sintering process, a highly reliable multilayer ceramic capacitor can be obtained. Will be obtained.

Here, the conventional multilayer ceramic capacitor having no heating element, the one obtained by changing the dielectric material in this conventional capacitor, the multilayer ceramic capacitor of the present invention having a heating element, and the capacitor of the present invention further have a heating element. The characteristics of the ceramic green sheet and the heating element having different thicknesses are shown in comparison with (Table 1) . The measuring method at this time is to measure the capacitance and the dielectric loss with a digital L
Using a CR meter model 4274A, measurement temperature 20
C., a measurement voltage of 1.0 Vrms, and a measurement frequency of 1 KHz. In addition, the temperature change rate of the capacitance was obtained by the following equation at the temperature of −25 ° C. and 85 ° C. based on the capacitance of 20 ° C. V = (C−Co) / Co × 100 V: Temperature change rate of capacitance (%) Co: Capacitance at 20 ° C. (nF) C: Capacitance at −25 ° C. and 85 ° C. (nF Further, the insulation resistance was measured using a HR meter model 4329A manufactured by Yokogawa Hewlett-Packard Co., Ltd. It was determined by measurement using DC for a measurement time of 1 minute. Further, the temperature characteristics of the capacitance are −25 ° C., −10 ° C.
° C, 10 ° C, 20 ° C, 40 ° C, 60 ° C, 80 ° C, 85 ° C
The capacitance was measured and determined at each temperature. When measuring various characteristics of the multilayer ceramic capacitor having the heating element, a power supply of 5 V. The measurement was performed by connecting an AC power supply of 1A.

FIG . 4 shows the measurement results of the temperature characteristics of the capacitance with the solid lines 13 and 14 for the samples 1 and 3, respectively.
Further, an example of the multilayer ceramic capacitor of the present invention will be described.
The solid line 12 shows the measurement result of the temperature characteristic of the capacitance of the sample 7.
Show.

[0029]

[Table 1]

As is clear from Table 1 and FIG. 4, the multilayer ceramic capacitor of Sample 1 using the conventional dielectric a and the multilayer ceramic capacitor of Sample 3 using the conventional dielectric b shown as comparative examples. Are 13 in FIG.
And 14 indicate the temperature characteristics of the capacitance indicated by the solid line, respectively, according to JIS C6429 standard FJ (capacity change rate is −25).
(+ 30% to -80% at ℃ to 85 ° C) and BJ (capacity change rate is ± 10% at -25 to 85 ° C). That is, the multilayer ceramic capacitor excellent specimen 3 temperature stability whereas the electrostatic capacitance is small and 30 nF, the multilayer ceramic capacitor of the sample 1 have poor temperature stability although the capacitance is large.

However, the multilayer ceramic capacitor of Sample 7 of the present invention realizes the same capacitance as the multilayer ceramic capacitor of Sample No. 1 in the same shape, and has a temperature stability of the multilayer ceramic capacitor of Sample No. 3. Is equivalent to

[0032] As described above, it has a heating element for self temperature control at a temperature higher than the temperature range, the self temperature control
A multilayer ceramic capacitor formed on a surface of a multilayer ceramic capacitor manufactured using a dielectric material having a high dielectric constant in the vicinity of the range has excellent temperature stability and a large capacitance.

As shown in Samples 4 to 12, by providing a buffer layer between each of the laminated ceramic capacitors and the heating element with a thickness of 10 μm or more of each material, the laminated ceramics such as dielectric loss and insulation resistance can be obtained. A multilayer ceramic capacitor that does not impair the reliability of the capacitor can be obtained.

In this embodiment, only the case where the heating element is disposed on one of the upper and lower sides of the multilayer ceramic capacitor is described. However, it is needless to say that the same effect can be obtained when the heating element is disposed on both the upper and lower sides.

Embodiment 2 Hereinafter, another embodiment of the present invention will be described.

FIGS. 5 and 6 are sectional views showing a part of the multilayer ceramic capacitor of the present invention. This figure 5,
6, the same parts as those in FIGS. 1 to 3 are denoted by the same reference numerals, and detailed description thereof will be omitted. In the figure, 15 is a condenser.
A buffer layer provided with the support layer that is not involved in the capacitance of the uppermost portion of the capacitors section, or a heating element buffer layer 16 is on top of the buffer layer 15 and the heating element 17 and the heating element metal conductor 18
Heating element is provided et made.

Hereinafter, a method for manufacturing the multilayer ceramic capacitor of the present invention will be described.

First, a green sheet of a dielectric material and a barium titanate-based positive temperature coefficient thermistor were formed in the same manner as in Example 1 .
Make a green sheet .

Next, 17 green sheets, and 7 green sheets on which a metal conductor was printed, on which a buffer layer was formed
A thickness of 7, 10 and 20 required number laminating glyceraldehyde <br/> Nshito dielectric such that [mu] m, as further thickness as a buffer layer of the heating element portion 7 becomes 10 and 20 [mu] m required number of green sheets of a barium titanate-based PTC thermistor
After laminating , and printing the green sheet with metal conductor printed
Two sheets , a 20 μm-thick barium titanate-positive thermistor metal conductor printed green sheet having a thickness of 20 μm as a heating element, and 17 20 μm-thick barium titanate-based positive-characteristic thermis green sheets as a heating element portion thereon After stacking, cut into individual pieces and fired at 1320 ° C. After obtaining a sintered body, in order to ensure the connection between the metal conductor and the terminal electrode, polishing the end faces of the sintered body, on both end surfaces of the polished sintered body, and a terminal electrode Ag Apply paste, 80
After baking at 0 ° C., a solder layer is formed by an electroplating method to manufacture a multilayer ceramic capacitor.

Here, the characteristics of each multilayer ceramic capacitor were measured in the same manner as in Example 1 described above. The results are shown in comparison with (Table 2).

[0041]

[Table 2]

[0042] As is clear from (Table 2), the multilayer ceramic capacitor Waso respectively of the sample 3 using the multilayer ceramic capacitor and dielectric c of the sample 1 using the conventional dielectric a shown as a comparative example F of JIS C6429 standard
J (Capacity change rate is + 30% to -25 ° C to 85 ° C)
-80%) and BJ (capacitance change ratio meets the characteristics standard ± 10%) at -25 ° C. to 85 ° C.. That is, the multilayer ceramic capacitor of Sample 3 having excellent temperature stability has a small capacitance of 30 nF, while the capacitance is 1 nF.
The multilayer ceramic capacitor of Sample 1 which is as large as 00 nF is
The capacitance change in the operating temperature range is large and the temperature stability is poor.

However, the multilayer ceramic capacitor of the sample 7, which is the multilayer ceramic capacitor of the present invention, realizes the same capacitance as that of the multilayer ceramic capacitor of the sample 1 in the same shape, and has a temperature stability of the multilayer ceramic capacitor of the sample 3. Same as capacitor.

As described above, the heating element for controlling the self-temperature at a temperature higher than the operating temperature range is used, and a dielectric having a high dielectric constant near the self-temperature control range is used. The laminated ceramic capacitor thus formed has excellent temperature stability and a large capacitance.

Further, as shown in Samples 4 to 12, by providing a buffer layer between the dielectric and the heating element with a thickness of 10 μm or more of each material, a multilayer ceramic capacitor having dielectric loss, insulation resistance and the like can be obtained. As a result, a multilayer ceramic capacitor that does not impair the reliability can be obtained.

In this embodiment, only the case where the heating element is disposed on one of the upper and lower sides of the capacitor section has been described.
It is needless to say that the same effect can be obtained by disposing both upper and lower parts, dividing the capacitor part, or disposing them in combination.

[0047]

As described above, according to the present invention, the provision of a heating element for controlling the element temperature of a capacitor to a constant value makes it possible to provide a small-sized, large-capacity device having excellent temperature stability, which was conventionally difficult. A multilayer ceramic capacitor can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the structure of a multilayer ceramic capacitor according to an embodiment of the present invention.

FIG. 2 is a perspective view of the multilayer ceramic capacitor.

FIG. 3 is an electric circuit diagram of the multilayer ceramic capacitor.

FIG. 4 is a temperature characteristic diagram of capacitance of the multilayer ceramic capacitor of the present invention and a conventional multilayer ceramic capacitor.

FIG. 5 is a sectional view showing the structure of a multilayer ceramic capacitor according to another embodiment of the present invention.

FIG. 6 is a perspective view of the multilayer ceramic capacitor.

FIG. 7 is a sectional view showing the structure of a conventional multilayer ceramic capacitor.

FIG. 8 is a temperature characteristic diagram of a dielectric constant of a dielectric having a high dielectric constant.

[Description of Signs] 1 Metal conductor 2 Dielectric layer 3 Terminal electrode 4,15 Buffer layer 5,16 Heating element buffer layer 6,17 Heating element 7,18 Heating element metal conductor 9 Terminal electrode

Claims (4)

(57) [Claims] 1. A metal conductor and the dielectric layer are laminated alternately to form a capacitor body, a multilayer ceramic capacitor having a heating element for controlling the temperature of the capacitor body of the capacitor body Nico constant. 2. The multilayer ceramic capacitor according to claim 1 , wherein a heating element is provided on at least one surface of the uppermost layer or the lowermost layer of the capacitor body. 3. The multilayer ceramic capacitor according to claim 1 , wherein a buffer layer is provided on at least one of the uppermost layer portion and the lowermost layer portion of the capacitor body, and a heating element is provided inside the buffer layer. 4. The multilayer ceramic capacitor according to claim 1 , wherein the heating element portion and the capacitor body have a structure separated by a buffer layer having a thickness of 10 μm or more formed of each material.