JPH06122544A - Dielectric material - Google Patents

Abstract

PURPOSE:To remarkably reduce particle diameter of crystal and improve specific resistance and DC bias characteristics of a dielectric material and temperature characteristics of dielectric constant thereof by substituting a part of Pb of a specific dielectric material consisting essentially of Pb(Mg1/3Nb2/3)O3-PbTiO3, etc., with La. CONSTITUTION:This dielectric material consists of a dielectric material containing Pb(Mg1/3Nb2/3)O3 and/or Pb(Mg1/2Nb1/2)O3 and PbTiO3 as main components and substituting a part of Pb with La. In producing this dielectric material, powders of starting raw materials are preferably mixed using a ball mill. After mixing, calcination is carried out. Preferably, the calcination is carried out at about 800-900 deg.C for about 1-4 hr. After calcination, the calcined material is crushed by the ball mill, etc. Average particle diameter of calcined powder is preferably properly controlled so as to provide crystal particles having desired diameter range after sintering.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to dielectric materials.

[0002]

2. Description of the Related Art Conventionally, BaTiO ₃ , BaSnO ₃ and CaT have been used as dielectric materials for various capacitors.
Based on iO ₃ , PbTiO _{3 and the} like, substituted solid solutions thereof and complex oxides containing these are used.

As an improvement of these dielectric materials, for example, Japanese Patent Publication No. 61-35144 discloses Pb.
(Mg _1/3 Nb _2/3 ) O ₃ -PbTiO ₃ -Pb (Mg
_1/2 W _1/2) high dielectric constant type ceramic composition obtained by adding a predetermined amount of MnO in O ₃ based compositions are disclosed. This composition
Since low temperature sintering is possible, it is not necessary to use an expensive noble metal for the internal electrodes when applied to a laminated ceramic capacitor. Moreover, the insulation resistance can be increased by adding MnO,
It is possible to reduce the dielectric loss.

By the way, in recent years, due to the progress of the thinning technology of the monolithic ceramic capacitor, it has become possible to reduce the thickness of the dielectric layer, which has been conventionally limited to about 20 μm, to about 10 μm or less. To make the layer thinner, a dielectric material with a smaller crystal grain size is required. Further, in order to reduce the thickness of the dielectric layer, a dielectric material having a larger specific resistance is required.

The dielectric material is also required to have good DC bias characteristics. When a DC bias voltage is applied to the dielectric material, the capacitance generally decreases, but it is desirable that the decrease rate be small, that is, that the DC bias characteristic be good.

Further, the Pb-based dielectric material has a larger relative permittivity than the BaTiO ₃ -based dielectric material, but since the temperature characteristic of the relative permittivity is generally poor, a material having a better temperature characteristic is desired. .

[0007]

SUMMARY OF THE INVENTION The present invention has been made under such circumstances, and Pb (Mg _1/3 Nb _2/3 )
O ₃ -PbTiO _{3 system, Pb (Mg 1/2 W 1/2)} O 3 -
PbTiO ₃ system, Pb (Mg _1/3 Nb _2/3 ) O ₃ -Pb
To significantly reduce the crystal grain size of the TiO ₃ —Pb (Mg _1/2 W _1/2 ) O ₃ -based dielectric material, and to improve the temperature characteristics of specific resistance, DC bias characteristics, and relative dielectric constant. To aim.

[0008]

These objects are achieved by the present invention described in (1) to (5) below. (1) Pb (Mg _1/3 Nb _2/3 ) O ₃ and / or P
A dielectric material containing b (Mg _1/2 W _1/2 ) O ₃ and PbTiO ₃ as main components, wherein a part of Pb is replaced with La. (2) The dielectric material according to (1) above, wherein the amount of substitution with La is 0.2 to 20 atomic% of Pb. (3) The molar ratio of Pb (Mg _1/3 Nb _2/3 ) O ₃ is x, P
The molar ratio of bTiO ₃ is y, Pb (Mg _1/2 W _1/2 ) O ₃
Where z is the molar ratio of
(X = 70, y = 0, z = 30), B (x = 0, y = 3
5, z = 65), C (x = 0, y = 100, z = 0) and D (x = 100, y = 0, z = 0) connected in this order on the side of the quadrangle and its inside ( However, the dielectric material according to the above (1) or (2), which has a composition represented by point C and line segment DA) as a main composition. (4) The dielectric material according to any one of (1) to (3), which has an average crystal grain size of 2 μm or less. (5) The dielectric material according to any one of (1) to (4) above, which contains MnO.

[0009]

In the present invention, Pb (Mg _1/3 Nb _2/3 ) O ₃ -PbTiO ₃ which can be sintered at low temperature and has good characteristics is used.
_{System, Pb (Mg 1/2 W 1/2)} O 3 -PbTiO 3 system, P
_{b (Mg 1/3 Nb 2/3} ) O 3 -PbTiO 3 -Pb (M
In the g _1/2 W _1/2 ) O ₃ -based dielectric material, the crystal grain size can be made extremely small by substituting a part of Pb with La. Further, by La substitution, the specific resistance can be increased, the DC bias characteristic can be improved, and the temperature characteristic of the relative dielectric constant can be improved.

Incidentally, Japanese Patent Laid-Open No. 4-12021 discloses that
Pb (Mg _1/2 W _1/2 ) O ₃ -Pb (Mg _1/3 Nb
_2/3 ) A dielectric porcelain composition in which a complex oxide containing MnO is added to a quaternary solid solution porcelain composition consisting of O ₃ —PbTiO ₃ —PbZrO ₃ is disclosed. According to the publication, a porcelain composition having a small crystal grain size is obtained, and in the examples, a sintered body having an average grain size of 2 μm is obtained. However, this is larger than the average particle size of the dielectric material of the present invention, and the publication does not disclose that the DC bias characteristics are improved.

[0011]

Specific Structure The specific structure of the present invention will be described in detail below.

The dielectric material of the present invention is Pb (Mg _1/3 N
b _2/3 ) O ₃ and / or Pb (Mg _1/2 W _1/2 ) O
₃ and PbTiO ₃ are main components, a part of Pb is replaced with La, and it has a perovskite structure. In addition,
Depending on the amount of La substitution, PbW may be used in addition to the perovskite phase.
Presence of O ₄ phase may be observed. Such a structure can be confirmed by X-ray diffraction.

The amount of substitution by La is 0.2 to the total amount of Pb.
It is preferably 20 atom%, particularly 1.0 to 15.0 atom%. If the substitution amount is less than the above range, the effect of the present invention becomes insufficient, and if the substitution amount exceeds the above range, the Curie point becomes low and the relative dielectric constant at room temperature becomes too small, so that practical properties tend to not be obtained. .

A preferred range of the main composition, that is, Pb (M
g _1/3 Nb _2/3 ) O ₃ , PbTiO ₃ and Pb (Mg
The preferable content ratio of _1/2 W _1/2 ) O ₃ is shown in the three-component composition diagram of FIG. 1. In the present invention, Pb (Mg _1/3 Nb _2/3 )
The molar ratio of O ₃ is x, the molar ratio of PbTiO ₃ is y, Pb
When the molar ratio of (Mg _1/2 W _1/2 ) O ₃ is z, FIG.
In the three-component composition diagram of A (x = 70, y = 0, z =
30), B (x = 0, y = 35, z = 65), C (x =
0, y = 100, z = 0) and D (x = 100, y =
It is preferable that the main composition is a composition represented on the side of a quadrangle that connects (0, z = 0) in this order and inside thereof (excluding point C and line segment DA). If the main composition deviates from the above range, the Curie point becomes too low, and the La-substitution further lowers the Curie point, so that a sufficient relative permittivity tends not to be obtained at room temperature. Further, by setting the main composition within the above range, it becomes possible to sinter in a low temperature range as described later.

A more preferable range of the main composition is shown in FIG.
In the three-component composition diagram of E (x = 80, y = 0, z =
20), F (x = 0, y = 40, z = 60), G (x =
0, y = 70, z = 30), H (x = 80, y = 20,
(z = 0) and D (x = 100, y = 0, z = 0) are connected in this order on the sides of the pentagon and inside (except for the line segment DE).

In the present invention, Pb (Mg _1/3 Nb _2/3 ) O
₃ and / or Pb (Mg _1/2 W _1/2 ) O ₃ and PbT
It is preferable to add MnO in addition to iO ₃ . M
By adding nO, the dielectric loss can be reduced and the specific resistance can be increased. The content of MnO is 1 based on the above main composition.
When the amount is 00% by weight, it is preferably 0.001 to 1.0% by weight. When the content is less than the above range, the effect of improving the dielectric loss and the specific resistance becomes insufficient, and when the content exceeds the above range, the dielectric constant tends to decrease and the dielectric loss and the specific resistance tend to deteriorate.

In the dielectric material of the present invention, by substituting La for Pb, the average crystal grain size of the sintered body can be easily adjusted to 2 μm or less, particularly 1.5 μm or less, and further 1.0 μm or less. it can. Incidentally, the average crystal grain size in this case, a straight line is drawn on the scanning electron micrograph of the fracture surface of the sintered body, and the length of the straight line is divided by the number of crystal grains hanging on this straight line. It is a value.

The dielectric material of the present invention can be applied to the dielectrics of various capacitors, but since the crystal grain size can be made extremely small, it is especially useful for multilayer ceramic capacitors,
Alternatively, it is particularly suitable for a laminated component including a capacitor section.

Next, a method of manufacturing the dielectric material of the present invention will be described. As a starting material, an oxide of a metal element that constitutes the dielectric material, such as PbO, Nb ₂ O ₅ , or Mg
O, WO ₃ , TiO ₂ , La ₂ O ₃ , MnO or the like may be used. In addition, carbonates such as MnCO ₃ and La ₂ (C ₂ O
₄ ) Other compounds such as oxalate such as ₃ may be used. The mixing ratio of the starting materials is selected so that the ratio of each metal element is the same as the final composition.

It is preferable to mix the powders of the starting materials by a wet method using a ball mill or the like. After mixing, calcination is performed. The calcination is preferably performed at a temperature of about 800 to 900 ° C. for about 1 to 4 hours. After calcination, it is crushed by a ball mill or the like. The average particle size of the calcined powder may be appropriately determined so that the crystal grain size in the range described above can be obtained after sintering. For example, the average particle size by a laser diffraction type particle size distribution meter is 0.6 to 2 μm, In particular, it is preferably 0.6 to 1.5 μm. If the average particle diameter exceeds the above range, it becomes difficult to reduce the crystal particle diameter.

Next, a binder such as polyvinyl alcohol is added to the calcined powder to shape it into a predetermined shape and then it is fired. In the present invention, 850 to 1050 ° C., particularly 900 to 9
Sintering in a low temperature range of 50 ° C is possible. The temperature holding time during firing may be usually about 1 to 2 hours.

When the dielectric material of the present invention is applied to a monolithic ceramic capacitor, a vehicle containing an organic binder and an organic solvent is added to the calcined powder to form a paste, and the paste is laminated by a printing method or a sheet method. Baked,
Further, a terminal electrode is provided to provide a laminated ceramic capacitor in which dielectric layers and internal electrode layers are alternately laminated. As the conductive material used for the internal electrode layer, an inexpensive low melting point metal such as Ag-based, Ni-based, or Al-based can be used.

Since the dielectric material of the present invention has a small crystal grain size as described above, the thickness of the dielectric layer of the monolithic ceramic capacitor can be set to 20 μm or less, particularly 5 to 10 μm. Capacitor can be realized. In addition,
The thickness of the internal electrode layer is not particularly limited, and may be a normal thickness, for example, about 1.5 to 3 μm.

The dielectric material of the present invention can be applied to various laminated components having a capacitor portion, such as a laminated LC composite component and a multilayer wiring board, in addition to the laminated ceramic capacitor.

[0025]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention.

PbO, Nb ₂ O ₅ and Mg as starting materials
Using O, WO ₃ , TiO ₂ and La ₂ O ₃ , the composition at point I (x = 15, y = 50, z = 35) in FIG. 1 (for those containing La, La was converted to Pb) was used. Weighed and blended so that Table 1 shows the Pb substitution amount of La. Then, these were wet mixed with a ball mill and calcined at 850 ° C. for 2 hours. The obtained calcined body was crushed with a ball mill, and the average particle size was 1.0 μm (measured by a laser diffraction type particle size distribution meter).
Of the calcined powder.

Next, an organic binder was added to the calcined powder, and the powder was molded at a pressure of ² ton / cm ² to obtain a disk-shaped molded product having a diameter of 12.5 mm and a thickness of 0.5 mm. 950 this molded body
Calcination was carried out for 2 hours. During firing, the compact and the calcined powder as a co-material were sealed in a bowl to prevent evaporation of Pb from the compact. Ag electrodes were formed on both main surfaces of the obtained sintered body, and the dielectric sample shown in Table 1 was obtained.

The electrical characteristics and average crystal grain size of these dielectric samples were measured. The results are shown in Table 1. The capacitance is measured at 1V and 1kHz, and the specific resistance is a value of 1 minute at 25V. The average crystal grain size was obtained by drawing a straight line on the scanning electron micrograph of the fractured surface of the sample and dividing the length of the straight line by the number of crystal grains lying on this straight line. The scanning electron micrographs of the cross sections of Sample Nos. 1 and 3 are shown in FIGS. 2 and 3, respectively.

[0029]

[Table 1]

From the results shown in Table 1, the effect of the present invention is clear. That is, in the sample in which a part of Pb was replaced with La, the electrical characteristics were improved as compared with the sample No. 1 without addition, and the average crystal grain size was extremely small, around 1 μm.

Preparation of Multilayer Ceramic Capacitor A dielectric layer paste containing a calcined powder, an organic binder, an organic solvent and a dispersant was prepared using a ball mill. The calcined powder was manufactured in the same manner as above. The composition of the calcined powder is as follows: J point (x = 5, y = 53, z = 4
In the composition of 2), 5 atom% of Pb is replaced with La, and the composition (La at the point K (x = 45, y = 25, z = 30) of FIG. (Without replacement).

Next, the dielectric layer paste was molded by a doctor blade method to obtain a green sheet. An electrode paste was printed on this green sheet, which was laminated and cut into a chip shape to obtain a green chip. The number of effective layers was 10. An Ag-Pd alloy with an atomic ratio of Ag: Pd = 70: 30 was used as the conductive material of the electrode paste.

After removing the binder from the green chip, the green chip was sealed in a casket together with the calcined powder of the common material, and baked at 950 ° C. for 2 hours. After firing, an indium-gallium electrode was applied as a terminal electrode to obtain a multilayer ceramic capacitor sample.

The DC bias characteristics of these were measured. The DC bias characteristic represents the rate of capacitance decrease when a DC voltage is applied. The temperature characteristics of the relative permittivity ε _s and the dielectric loss tan δ of the La-substituted sample were measured. The results are shown in FIGS. 4, 5 and 6, respectively. The number of measurements of ε _s and tan δ was 2, respectively, and all the measurement results are shown in FIGS. 5 and 6.

From these results, the effect of the present invention is clear. That is, as shown in FIG. 4, the La substitution suppresses the decrease in capacitance when a DC voltage is applied. In addition, as shown in FIGS. 5 and 6, JIS C 64
E characteristic capacitance change rate (-25 to 85
C, reference temperature 20 ° C., capacitance deviation −55 to 20%) and dielectric loss (5.0% or less at reference temperature 20 ° C.) are satisfied.

In each of the above samples, when 1% by weight of MnO was added to the main composition, a decrease in dielectric loss and an increase in specific resistance were observed.

In addition, Pb (Mg _1/3 Nb _2/3 ) O ₃ -P
bTiO ₃ system and Pb (Mg _1/2 W _1/2 ) O ₃ -Pb
As for the TiO ₃ -based composition, the La substitution experiment was conducted in the same manner as described above, and as a result, it was confirmed that the electrical characteristics were improved and the average crystal grain size was reduced, as in each of the samples.

[Brief description of drawings]

FIG. 1 is a three-component composition diagram showing the main composition of a dielectric material of the present invention.

FIG. 2 is a drawing-substitute photograph showing a crystal structure, which is a scanning electron microscope photograph of a conventional dielectric material.

FIG. 3 is a drawing-substituting photograph showing a crystal structure, which is a scanning electron microscope photograph of a dielectric material of the present invention.

FIG. 4 is a graph showing DC bias characteristics of a laminated ceramic capacitor to which the present invention is applied and a conventional laminated ceramic capacitor.

FIG. 5 is a graph showing temperature characteristics of relative permittivity ε _s of a laminated ceramic capacitor to which the present invention is applied.

FIG. 6 is a graph showing temperature characteristics of dielectric loss tan δ of the laminated ceramic capacitor to which the present invention is applied.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Furubayashi 13-13-1 Nihonbashi, Chuo-ku, Tokyo TDC Corporation

Claims (5)

[Claims] 1. Pb (Mg _1/3 Nb _2/3 ) O ₃ and / or
Or _{Pb (Mg 1/2 W 1/2} ) a dielectric material mainly composed of the O ₃ and PbTiO _3, a dielectric material, wherein a part of Pb is substituted with La. 2. The amount of substitution with La is 0.2 to 20 of Pb.
The dielectric material of claim 1, wherein the dielectric material is atomic%. _3. The molar ratio of Pb (Mg _1/3 Nb _2/3 ) O ₃ is x, the molar ratio of PbTiO ₃ is y, and Pb (Mg _1/2 W _1/2
) When the molar ratio of O ₃ is z, in the three-component composition diagram, A (x = 70, y = 0, z = 30), B (x = 0, y = 35, z = 65), C ( x = 0, y = 100, z = 0) and D (x = 100, y = 0, z = 0) are connected in this order on the side of the quadrangle and its inside (however, point C and line segment DA are The dielectric material according to claim 1 or 2, which has a composition represented by (excluding) as a main composition. 4. The dielectric material according to claim 1, which has an average crystal grain size of 2 μm or less. 5. The dielectric material according to claim 1, which contains MnO.