High Frequency Wave Absorbing Ceramics

1. Field of the Invention

This invention concerns high frequency wave absorbing ceramics for absorbing high frequency electromagnetic waves.

The ceramics according to this invention can be used, for example, as an EMI (electromagnetic interference) preventive filter for interrupting high frequency waves intruding into electronic circuits.

2. The Prior Art

Heretofore, dielectric materials such as barium titanate or magnetic materials such as ferrite have been used for the EMI preventive filters.

However, these materials involve drawbacks in that the attenuating band width at high frequency region is narrow, the high frequency interrupting effect is poor, etc. These drawbacks are attributable to the low specific dielectric constant at high frequency.

This invention has been achieved in order to improve the foregoing drawbacks in the materials of the prior art and it is an object of this invention to provide a novel high frequency wave absorbing material having a large specific dielectric constant in a frequency region from 1 to 100 MHz and a large dielectric loss in a frequency range from 100 MHz to 1 GHz, that is, providing a significant high frequency interrupting effect in the frequency range from 1 MHz to 1 GHz.

The high frequency wave absorbing ceramics of the present invention comprises a ternary composition comprising from 55 to 85 mol % of lead iron niobate Pb(Fe.sub.1/2 Nb.sub.1/2)O.sub.3, from 10 to 40 mol % of lead iron tungstate Pb(Fe.sub.2/3 W.sub.1/3)O.sub.3 and not more than 20 mol % of lead nickel tantalate Pb(Ni.sub.1/3 Ta.sub.2/3)O.sub.3 based on the total 100 mol % of a composition composed of lead iron niobate Pb(Fe.sub.1/2 Nb.sub.1/2)O.sub.3, lead iron tungstate Pb(Fe.sub.2/3 W.sub.1/3)O.sub.3 and lead nickel tantalate Pb(Ni.sub.1/3 Ta2/3)O.sub.3.

FIG. 1 is a ternary phase diagram showing the range of the composition ratio of the ternary composition according to this invention.

FIG. 2 is a graph showing the characteristics of the specific dielectric constant of the ternary composition relative to the third ingredient composition ratio x, using the binary composition ratio y as a parameter.

FIG. 3 is a graph showing the characteristics of the specific dielectric constant of the ternary composition relative to the binary composition ration y, using the ternary composition ratio x as a parameter.

FIG. 4 is a graph showing the characteristics of the specific dielectric constant of the ternary composition when x is 0.05 as shown in FIG. 3.

FIG. 5 is a graph showing the characteristics of the specific dielectric constant of the ternary composition when x is 0.025 and 0.15 as shown in FIG. 3.

FIG. 6 is a graph showing the frequency characteristics of the specific dielectric constant for the binary composition (No. 1) and for the ternary composition (No. 7).

FIG. 7 is a perspective view showing the structure of a high frequency cut-off filter according to the first application example using the material of this invention.

FIG. 8 is a perspective view showing the state of high frequency cut-off filter according to the first application example disposed to the connector portion.

FIG. 9 is a perspective view showing the state of the high frequency cut-off filter according to the second application example disposed to the connector portion.

FIG. 10 is a perspective outer view for the high frequency cut-off filter according to another modification embodiment.

This invention concerns high frequency wave absorbing ceramics of a ternary composition comprising from 55 to 85 mol % of lead iron niobate Pb(Fe.sub.1/2 Nb.sub.1/2)O.sub.3, from 10 to 40 mol % of lead iron tungstate Pb(Fe.sub.2/3 W.sub.1/3)O.sub.3 and not more than 20 mol % of lead nickel tantalate Pb(Ni.sub.1/3 Ta.sub.2/3)O.sub.3.

According to this invention, the specific dielectric constant of a binary composition comprising lead iron niobate Pb(Fe.sub.1/2 Nb.sub.1/2)O.sub.3 and lead iron tungstate Pb(Fe.sub.2/3 W.sub.1/3)O.sub.3 is improved by incorporating thereto a further third ingredient.

The ternary composition within the above specified range has a specific dielectric constant of from 10,000 to 20,000 at 1 MHz at the room temperature.

In the case of using the composition according to this invention as the high frequency wave absorbing filter, it is required that the specific dielectric constant at 1 MHz is not less than 8,000 in order to obtain a satisfactory high frequency cut-off property (refer to Japanese Patent Application No. 147,343/1984).

Accordingly, the composition ratio in the material according to this invention is determined such that it has a specific dielectric constant not less than about 10,000 at 1 MHz and thus providing a sufficient high frequency wave absorbing effect.

The composition outside of the above-mentioned range is not suitable as the high frequency wave absorbing material since the specific dielectric constant at 1 MHz is less than 10,000. Particularly, the material within the range inside the quadrangle ABCD in the ternary phase diagram shown in FIG. 1 has a specific dielectric constant of not less than 13,000 and is more suitable as the high frequency wave absorbing material.

Since the material according to this invention comprises a ternary composition having a high specific dielectric constant within the frequency region of from 1 MHz to 100 MHz, it is excellent in the high frequency wave absorbing effect.

This invention will now be described referring to specific example. As the starting material, 4 mol of lead oxide powder (PbO), 1 mol of iron oxide powder (Fe.sub.2 O.sub.3) and 1 mol of niobium oxide powder (Nb.sub.2 O.sub.5) were blended, and mixed in a wet manner to thereby obtain a material of lead iron niobate Pb(Fe.sub.1/2 Nb.sub.1/2)O.sub.3 (hereinafter referred to as "the first ingredient").

Further, 3 mol of lead oxide powder (PbO), 1 mol of iron oxide powder (Fe.sub.2 O.sub.3) and 1 mol of tungsten oxide powder (WO.sub.3) were blended and mixed in a wet manner into a material of lead iron tungstate Pb(Fe.sub.2/3 W.sub.1/3)O.sub.3 (hereinafter referred to as "the second ingredient").

Furthermore, 4 mol of lead oxide powder (PbO), 1 mol of tantalum oxide powder (Ta.sub.2 O.sub.5) and 1 mol of nickel oxide powder (NiO) were blended and mixed in a wet manner into a material of lead nickel tantalate Pb(Ni.sub.1/3 Ta.sub.2/3)O.sub.3 (hereinafter referred to as "the third ingredient").

Then, these three types of powder mixtures were respectively kneaded in a wet manner for 24 hours each in a polyethylene jar incorporating with agates, then calcined at about 800.degree. C. for one hour, followed by pulverization to thereby obtain the first ingredient powder, the second ingredient powder and the third ingredient powder respectively.

Then, the first ingredient powder, the second ingredient powder and the third ingredient powder were blended respectively so as to provide the composition ratios: No. 1-No. 15 shown in Table, and mixed in a wet manner to obtain various powdery specimens. Then, after pelletizing the respective powdery specimens with paraffin and then molding under a pressing pressure of 500 kg into a cylinder sized 10 mm .phi..times.5 mm, they were calcined at a temperature from 1,000.degree. to 1,150.degree. C. for one hour. The molding products were baked at the both end faces thereof with silver paste to form electrodes which used for the measurement of the frequency characteristics of the dielectric constant. The frequency characteristics were measured by using a vector impedance analyzer.

For the specimens No. 1-No. 15, the results of the measurement for the specific dielectric constant at 1 MHz under the room temperature are shown in Table.

FIG. 2 shows the characteristics of the specific dielectric constant of the ternary composition represented as:

(1-x){(1-y)Pb(Fe.sub.1/2 Nb.sub.1/2)O.sub.3 -yPb(Fe.sub.2/3 W.sub.1/3)O.sub.3 }-xPb(Ni.sub.166 Ta.sub.2/3)O.sub.3, relative to the third ingredient composition molar ratio x (hereinafter referred to as x) for the ternary system using the composition molar ratio y (hereinafter referred to as y) for the binary system as a parameter.

FIG. 3 shows the characteristics of the specific dielectric constant relative to the composition ratio y using the composition ratio x as a parameter.

FIG. 4 and 5 each represent, respectively, those graphs in the cases of x=0.05, x=0.025-0.15, each extracted from those shown in FIG. 3.

FIG. 6 shows the frequency characteristics of the specific dielectric constant for specimens No. 1 and No. 7.

As can be seen from Table and FIG. 2, relative to the specific dielectric constant of the binary composition: 75 Pb (Fe.sub.1/2 Nb.sub.1/2)O.sub.3 -25 Pb(Fe.sub.2/3 W.sub.1/3)O.sub.3 (specimen No. 1, y=0.25), the specific dielectric constant of the ternary composition is increased by incorporating thereto not more than about 17 mol % of Pb(Ni.sub.1/3 Ta.sub.2/3)O.sub.3 as the third ingredient. x is preferably from 0.01 to 0.15 and, most preferably, 0.05. It can further been seen from FIGS. 2 and 3 that the increasing tendency of the specific dielectric constant with the incorporation of the third ingredient is also dependent on y.

As shown in FIG. 2, when x is more than zero and not more than 0.2 at y=0.25, the specific dielectric constant is not less than about 10,500 and, particularly, when x is more than zero and not more than 0.17 at y=0.25, the specific dielectric constant takes an large value of not less than about 12,000. When x is from 0.015 to 0.13 at y=0.25, the specific dielectric constant is not less than about 15,000. When x is from 0.05 to 0.15 at y=0.15, the specific dielectric constant is from 11,000 to 14,000. Further, when x is from 0.025 to 0.15 and y is from 0.25 to 0.35, the specific dielectric constant may be not less than about 13,000.

Further, as shown in FIGS. 4-6, in a case where the ternary composition is expressed in the same composition scheme as described above, y has a relationship to x as described below.

Specifically, as shown in FIG. 4, when y is from 0.13 to 0.41 at x=0.05, the specific dielectric constant is not less than about 10,000 and, particularly, when y is from 0.18 to 0.34 at x=0.05, the specific dielectric constant shows an extremely high value as large as not less than about 15,000. As shown in FIG. 5, when y is from 0.20 to 0.35 at x=0.025, the specific dielectric constant is from 13,000 to 17,000. When y is from 0.15 to 0.35 at x=0.15, the specific dielectric constant is from about 13,000 to 14,000. Further, as shown in FIG. 3, when x is from 0.025 to 0.15 and y is from 0.20 to 0.35, the specific dielectric constant may be not less than about 13,000 and, particularly, when x is from 0.025 to 0.05 and y is from 0.2 to 0.31, the specific dielectric constant may be extremely large as from about 15,000 to 20,000.

The reason for the improvement is the specific dielectric constant by the incorporation of the third ingredient can be considered as below.

That is, it can be considered that the dielectric dispersion is low at not more than 1 MHz and the attenuation in the specific dielectric constant is low and that the absolute value for the specific dielectric constant has been improved. Further, as can be seen in FIG. 6, it has a higher specific constant than that of the binary composition also within a range from 1 MHz to 100 MHz (the dielectric constant is approximately the same at a frequency region of higher than 100 MHz). Further, since the attenuation amount of the specific dielectric constant is larger in the ternary composition at the frequency region of higher than 1 MHz, the dielectric loss is larger and, accordingly, the heat loss at high frequency is also larger in the frequency region of higher than 1 MHz.

Those compositions included within the quadrangle A--B--C--D (including the boundary line) in the ternary phase diagram in FIG. 1 are particularly satisfactory having a high specific dielectric constant of not less than 13,000 in such a high frequency region. Further, if the ratio is out of the range of claim 1, the specific dielectric constant at 1 MHz is reduced and it is not suitable as the high frequency wave absorbing material.

Then, an application example of a high frequency cut-off filter using the material according to this invention is shown. FIG. 7 is a perspective view showing the constitution of a high frequency cut-off filter according to the one application example (a first application example).

A dielectric spacer 10 comprises the ternary composition according to this invention. An electrode is formed at one main surface 10a of the dielectric spacer 10 by printing to bake a silver paste in a rectangular form and another electrode is formed at the opposing second main surface 10b thereof by printing to bake a silver paste entirely over the end face. One end face of a grounding electrode 14 is disposed with the dielectric spacer 10 so as to be in contact with the another electrode, while the other end face is in contact with other dielectric spacer 11 of the same structure as that of the dielectric spacer 10. A plurality of U-shaped lead pins 12 are disposed so as to be in connection with the electrode formed on the first main surface of the dielectric spacers 10, 11, which constitute the signal line electrodes.

In the high frequency cut-off filter of such a constitution, signals are inputted from one terminal 123 of the lead pins 12, in which the high frequency signals are bypassed by way of the dielectric spacer 10 to the grounding electrode 14, while only the signals at low frequency are taken out from an output terminal 125 as the other terminal of the lead pins 12.

In this way, the high frequency noise component can be cut-off.

FIG. 8 is a perspective view showing the high frequency cut-off filter in the first application example mounted to a connector portion 6. The grounding electrode 14 is connected to a metal case 7 and each one end of the lead pins 12 is connected to a signal line 15, while each of the other ends is connected to a signal line 16 on a circuit board 20 of the electronic device. In this way, the high frequency cut-off filter can be incorporated into a connector portion of electronic equipments.

FIG. 9 is a perspective view where a high frequency cut-off filter according to another application example (a second application example) is disposed to the connector portion 6. The signal line electrode 12 is put between the dielectric spacers 10 and 11. The lower surface of the dielectric spacer 10 is in contact with the grounding electrode 14. The grounding electrode 14 is disposed by way of an insulator plate 19 on a circuit board 20 and further connected electrically to a metal casing 7. Further, a grounding electrode 14a is formed also on the upper surface of the dielectric spacer 11, which is connected electrically to the metal case 7 in the same manner as described above.

In this way, the signal line electrode is sandwitched between a plurality of dielectric spacers to constitute a parallel capacitor form.

Further, it is also possible to apply resin potting the filters of these application examples to constitute as shown in FIG. 10.