JPH0662529U - Multilayer ceramic capacitor - Google Patents

Abstract

(57) [Abstract] [Purpose] Multilayer ceramic capacitors have various features. Since they have a ceramic material with a high dielectric constant, high capacitance can be obtained in a small volume and frequency characteristics are not bad. However, when trying to pass a high-frequency signal of about several gigahertz, the passing characteristic may be deteriorated. Therefore,
It is an object of the present invention to improve the structure of a multilayer ceramic capacitor so that good pass characteristics can be obtained even at such a high frequency. [Structure] Each layer is formed by the thin film of the internal electrode 1 and the dielectric ceramic sheet 3, and many layers are stacked to form a laminated ceramic capacitor. At least one of these layers is of low dielectric constant type. It is made of a ceramic material, a high-frequency signal is passed through this layer, and the other layers are made of a high dielectric constant material so that a large capacitance is obtained.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention is intended to improve the structure of a multilayer ceramic capacitor that is often used as an electrical element of a printed circuit board, and to improve the high frequency transmission characteristics of such a capacitor.

[0002]

[Prior art]

 Multilayer ceramic capacitors are well known, and one example of the structure thereof is shown in FIGS. 2 (a) and 2 (b) and FIGS. 3 (a) and 3 (b). In order to protect the structure shown in FIG. 2, the one shown in FIG. 3 is entirely resin-coated except for a part of the external electrode, and a lead is attached to the external electrode. Is also a product.

The multilayer ceramic capacitor shown in FIGS. 2A and 2B will be described. As shown in FIG. 2B, a thin plate-shaped dielectric ceramic sheet 3 and a metal film on the surface of the sheet. The integrated ones with the internal electrodes 2 are stacked in multiple layers, and every other internal electrode 2 is connected to the left and right external electrodes 2A and 2B, and the film is formed as shown in (a) of FIG. The dielectric ceramic sheet 3 between the respective plates of the inner electrode 1 is formed.

Such a multilayer ceramic capacitor usually uses the dielectric ceramic sheet 3 made of the same material in order to reduce the manufacturing cost. In order to reduce the physical size of the multilayer capacitor to obtain the required capacitance, it is often the case that the dielectric ceramic sheet 3 mainly composed of high dielectric constant BaTiO ₃ (barium titanate) is used. ing.

A capacitor using ceramics as a dielectric is generally characterized by good heat dissipation, a long life, and a high dielectric constant, and has good frequency characteristics, but it is used at several KHz to several tens of MHz. There is a drawback in that the pass characteristic deteriorates in the high frequency region when the width is in the range of several kHz to several GHz regardless of the frequency range. Therefore, it has been attempted to avoid this drawback by using two or more such multilayer capacitors in combination in parallel.

[0006]

[Problems to be solved by the device]

 Generally, a capacitor having a ceramic as a dielectric has a good frequency characteristic, but its transmission characteristic deteriorates when a high frequency signal of about several GHz is obtained. The means for avoiding this is to use two or more multilayer capacitors in parallel, because the inductive connection and stray capacitance that are added to make them parallel are newly added. Unnecessary resonance points occur irregularly and unexpected frequency characteristics with insufficient pass characteristics occur, so it is difficult to obtain the desired high frequency pass characteristics, and only two multilayer ceramic capacitors are used. There was more than the drawback of requiring a place, which is a drawback for use.

Therefore, the present invention has an object to improve the high-frequency transmission characteristics of the multilayer capacitor and eliminate such defects and defects.

[0008]

[Means for Solving the Problems]

In order to achieve the above object, the present invention uses a low dielectric constant material, such as TiO ₂ (titanium oxide), for at least one of the dielectric ceramic sheets stacked in a conventional multilayer ceramic capacitor. A high frequency signal is allowed to pass through this low dielectric constant layer portion to improve the high frequency transmission characteristics without reducing the total capacitance of the multilayer ceramic capacitor.

The layer using this low dielectric constant material is not limited to one layer, and it may be combined with the adjacent layer to form two layers, or more continuous layers adjacent to each other. This may be done for all layers of the group. However, since it is necessary to obtain the capacitance required for the multilayer capacitor in a small volume, it is necessary to make most of the layer using a high dielectric constant material such as BaTiO ₃ (barium titanate). is there. Further, it is conceivable that two layers using a low dielectric constant material are used and the layer between the two layers is made of a high dielectric constant material. When the two layers are separated, the external electrode becomes a pass-through circuit for high-frequency signals that connects these layers, and this slight pass-through circuit has unnecessary inductivity and gives a bad influence to high frequencies around GHz. Therefore, the two layers that allow high-frequency signals to pass through should not be separated from each other.

However, it suffices to use an intermediate dielectric constant material without suddenly making the layer next to the layer using the low dielectric constant material a high dielectric constant material. Rather, it is often the case that the use of an intermediate one does not deteriorate the high-frequency transmission characteristics and makes its manufacture easier.

Then, the best high-frequency characteristics can be obtained by mounting the layer using the material having the low dielectric constant on the print substrate so as to be the lowermost layer of the laminated layers. This is because it is the best way to prevent unnecessary inductive components or stray capacitances from occurring by making the circuit surface of the printed circuit board and the surface of the multilayer capacitor layer that passes high-frequency signals coincide. If the center layer of the multilayer capacitor is a layer that allows high-frequency signals to pass through, the multilayer capacitor would have to penetrate the printed circuit board in order to match the two surfaces as above. This is not desirable because is generally inappropriate.

When one monolithic ceramic capacitor is constructed by including different materials in this way, the capacitor is cracked due to the difference in the material, for example, the contraction rate after sintering, that is, the difference in thermal expansion coefficient. Therefore, it is necessary to pay careful attention to the selection of the material, but by mixing various materials, it is possible to obtain a material that has a dielectric constant that is quite different, but that has the same coefficient of linear expansion as, for example, barium titanate. Since a low-dielectric-constant ceramic material that can be sintered is known, the intended monolithic ceramic capacitor can be obtained if the dimensions of the monolithic capacitor and the assumptions for producing it are sufficiently devised.

[0013]

【Example】

FIG. 1 shows an embodiment of the present invention. A ceramic sheet 3 mainly composed of low dielectric constant TiO ₂ (titanium oxide) is used for the material a in the figure, and high dielectric constant BaTiO ₃ (barium titanate) is mainly composed for the materials b, c and d. It was manufactured by using the dielectric ceramic sheet 3. The structures and manufacturing methods of the external electrode 2 and the internal electrode 1 are the same as those of the conventional one. Of course, the resin coating and the manufacturing method for the chip type capacitor or the lead type capacitor are the same as the conventional ones, and any type may be used.

If the permittivities of the materials a, b, c, and d are a ′, b ′, c ′, and d ′, in this case, a ′ <b ′ = c ′ = d ′, , A ′ <b ′ ≦ c ′ ≦ d ′.

[0015]

[Effect of device]

 Since the present invention is constructed as described above, a large capacitance is obtained in the high dielectric constant layer portion, and a low frequency signal is passed in this portion. Since a high-frequency signal is passed through the low-dielectric-constant layer portion provided in one place, it is possible to improve the pass characteristic in the high-frequency portion without lowering the electrostatic capacitance as compared with the conventional one. it can.

Further, the circuit surface of the printed circuit board and the surface of the layer through which a high frequency signal passes are made to coincide with each other, that is, they are coplanar, so that the multilayer ceramic capacitor is mounted on the printed circuit board without deteriorating the high frequency transmission characteristics. be able to.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of a multilayer ceramic according to the present invention.

FIG. 2 is a perspective view of a main part of a conventional laminated ceramic. (A) A perspective view of a main part of the main body. (B) The perspective view which decomposed | disassembled the inside.

FIG. 3 is a diagram showing a mold of a laminated ceramic product according to the related art. (A) Chip type. (B) Lead type.

[Explanation of symbols]

 1 Internal electrode 2 External electrode 3 Dielectric ceramics a, b, c, d Ceramics material

Claims (4)

[Scope of utility model registration request] 1. In a multilayer ceramic capacitor in which dielectric ceramics and internal electrodes are alternately stacked, the dielectric constant of a continuous group of dielectric ceramics including at least one layer is made of a material having a low dielectric constant. A multilayer ceramic capacitor characterized in that the dielectric constant of the other layers of the dielectric ceramic is made of a material having a higher dielectric constant than this. 2. The layer according to claim 1, wherein among layers composed of a material having a high dielectric constant, a layer closer to a layer composed of a material having a low dielectric constant has a material having an equal or lower dielectric constant. Multilayer ceramic capacitor. 3. The multilayer ceramic capacitor according to claim 2, wherein the layers having a high dielectric constant are all made of a material having a same dielectric constant. 4. The multilayer ceramic capacitor according to claim 1, wherein a layer made of a material having a low dielectric constant is used as a layer at one end of the stack, and the layer at one end is the bottom layer of the stack. .