JPH0644406B2 - High permittivity dielectric ceramic composition for microwave - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high dielectric constant dielectric ceramic composition for microwaves, and in particular, it is useful for miniaturization of filters and the like used in the microwave region. The present invention relates to a high dielectric constant dielectric ceramic composition for waves.

[Outline of Invention]

The present invention is represented by the general formula xBaO · y (K ₂ O · Bi ₂ O ₃ ) · zNd ₂ O ₃ · (6-z) TiO ₂ ,
By using a composition whose composition range is 0.88 ≤ x ≤ 0.98 0.056 ≤ y ≤ 0.110 0.95 ≤ z ≤ 1.11 as the main component and adding 0.5 wt% or less of Cr ₂ O ₃ as an accessory component, microwave Dielectric constant It is intended to improve the relative dielectric constant of the dielectric ceramic composition, reduce the dielectric loss in the microwave region, and improve their temperature characteristics.

[Prior Art] Conventionally, dielectrics have been used even in the microwave region, for example, for impedance matching elements, dielectric resonators, dielectric antennas, and the like in microwave circuits.

In recent years, with the progress of circuit technology in the microwave region, the expansion of the application range and the used frequency band, and the like, there has been a demand for miniaturization of elements, particularly in the microwave region having a relatively long wavelength.

From such a background, a dielectric material for microwaves satisfying the following requirements is desired.

That is, it is necessary to have a high dielectric constant epsilon _r of the dielectric relative to (i) miniaturization purposes. For example, the volume of a filter or the like is set to a dielectric material for a conventional dielectric resonator (relative permittivity ε _r about 30).
˜40), it is desirable that at least the relative permittivity ε _r be 80 or more in order to make it approximately 1/3 or less.

(Ii) Temperature coefficient τ of resonance frequency when the filter is constructed
It is desirable that _f is at least equal to or higher than the temperature coefficient of the other component elements. For example, in the case of a microstrip line filter formed on a high-purity aluminum substrate (temperature coefficient of relative permittivity τ = + 120 ppm / ° C.) which is often used as a substrate of microwave IC, the temperature coefficient τ _f of resonance frequency is approximately −. 55 ppm / ° C. Therefore, it is preferable that τ _f ≦ ± 50 ppm / ° C.

(Iii) It is desirable that the Q value of the filter is as large as possible in terms of the structure of the filter. However, the Q of the dielectric material used in the unloaded state, that is, Q _o , is effect in consideration of, _{Q o} ≦ 2000 substantially determined as a value only the conductor loss, for example in 3~4GHz
Is desirable.

However, it has been difficult for conventional dielectric materials to simultaneously satisfy the above requirements. For example, as a dielectric material having a relatively large relative permittivity ε _{r and} good temperature characteristics, a dielectric composition for a temperature compensation capacitor is conventionally known, but these compositions have a frequency range of about several MHz. However, although the dielectric loss was small, the dielectric loss became too large in the microwave region, and the above requirements could not be satisfied. Specifically, in the BaTiO ₃ —Y ₂ O ₃ · TiO ₂ —TiO ₂ system composition, Q _{o at} 1 MHz is about 1670, but 3 GHz
The Q _o at 160 is about 160.

[Problems to be solved by the invention]

Therefore, the present invention provides a high dielectric constant dielectric material for microwaves satisfying the above-mentioned requirements for dielectric properties, that is, the relative dielectric constant ε _r ≧ 80, the temperature coefficient τ _f ≦ ± 50 ppm, and the Q _o ≧ 2000 at a frequency of 3 to 4 GHz. An object is to provide a body porcelain composition.

[Means for solving problems]

The present inventors have developed a high-permittivity dielectric ceramic composition for microwaves, and as a result of earnest research over a long period of time,
Of the O-Nd ₂ O ₃ -TiO ₂ -based dielectric ceramic composition, BaO ・ Nd ₂ O ₃
・ A dielectric ceramic composition in which a part of BaO is replaced with K ₂ O + Bi ₂ O ₃ in the composition region near 5TiO ₂ and a dielectric ceramic composition in which a trace amount of Cr ₂ O ₃ is added to this purpose The inventors have found that they are compatible and satisfy the above requirements, and have completed the present invention.

That is, the present invention is represented by the general formula xBaO · y (K ₂ O · Bi ₂ O ₃ ) · zNd ₂ O ₃ · (6-z) TiO ₂ , and its composition range is 0.88 ≦ x ≦ 0.98 0.056 ≦ y ≦ It is characterized in that a composition satisfying 0.110 0.95 ≦ z ≦ 1.11 is contained as a main component, and 0.5% by weight or less of Cr ₂ O ₃ is added as a subsidiary component.

In the high dielectric constant dielectric ceramic composition for microwaves of the present invention, the molar fraction x of BaO is set to 0.88 to 0.98 because the dielectric constant ε _r is smaller than 80 when the molar fraction x is less than 0.88. This is because the temperature coefficient τ _f becomes too large, and when the mole fraction x exceeds 0.98, the dielectric loss becomes too large and inappropriate.

Further, the mole fraction y of K ₂ O · Bi ₂ O ₃ is set to 0.056 to 0.110, because the temperature coefficient τ _f becomes too large when the mole fraction y is less than 0.056, and the dielectric loss is exceeded when it exceeds 0.110. Is too large, or the dielectric constant ε _r is smaller than 80, which is unsuitable. For example, {0.9BaO ・ y (K ₂ O ・ Bi ₂ O ₃ )} ・ Nd ₂ O ₃・ 5TiO ₂ and K ₂ O
・ When the change of the temperature coefficient τ _f was investigated while changing the mole fraction y of Bi ₂ O ₃ , as shown in FIG. 1, when y = 0.056 or more, the temperature coefficient τ _f showed an extremely small value of about +25 ppm. Turned out to show. Similarly, when the change in Q _o at 4 GHz was examined, it was found that 0.056 ≦ y ≦ 0.1 as shown in FIG.
The maximum value was shown in the range of 10, and the size was 2000 or more.

The molar fraction z of Nd ₂ O ₃ is set to 0.95 to 1.11 if the molar fraction z is less than 0.95, the dielectric loss becomes too large or the temperature coefficient τ _f becomes too large. This is because the loss is too large or the dielectric constant ε _r is smaller than 80, which is unsuitable. For example, {0.9BaO · 0.1 (K ₂ O · Bi ₂ O ₃ )} · zNd ₂ O ₃ · (6-z) TiO ₂ is used, and the temperature coefficient τ _f is changed by changing the mole fraction z of Nd ₂ O _3. As a result of investigating the changes in the above, it was found that the temperature coefficient τ _f ≈ + 25 ppm was achieved when z ≦ 0.95, as shown in FIG. Similarly, when the change in Q _o at 4 GHz was examined,
As shown in the figure, it has been found that the maximum value is shown in the vicinity of z = 1.0, and 0.95 ≦ z ≦ 1.10 is required to set the value to 2000 or more.

On the other hand, addition of Cr ₂ O ₃ is effective in improving the sinterability. For example, with and without addition of 0.2% by weight of Cr ₂ O ₃ to a dielectric composition of {0.9BaO ・ 0.1 (K ₂ O ・ Bi ₂ O ₃ )} ・ Nd ₂ O ₃・ 5TiO _2. was examined the relationship between the density ρ of the sintered body obtained respectively the firing temperature, as shown in FIG. 5, Cr ₂ O
It was found that the addition of ₃ can lower the firing temperature. However, since the addition of Cr ₂ O ₃ causes an increase in dielectric loss (a decrease in Q _o ) and an increase in temperature coefficient τ _f , the addition amount thereof is preferably suppressed to 0.5% by weight. For example, when Cr ₂ O ₃ is added to the composition of {0.9BaO · 0.1 (K ₂ O · Bi ₂ O ₃ )} · Nd ₂ O ₃ / 5TiO ₂ and the addition amount is gradually increased, As shown in FIG. 6, the temperature coefficient τ _f also increased, and this tendency was remarkable especially when the addition amount exceeded 0.5% by weight. Similarly, as the amount of Cr ₂ O ₃ added is increased, as shown in Fig. 7, Q _o gradually decreases, and the amount added is 0.5% by weight.
It was found that Q _o <2000 when the value exceeded.

Therefore, the dielectric ceramic composition of the present invention is
It can be prepared by mixing the respective raw material powders of ₃ , Nd ₂ O ₃ , TiO ₂ , K ₂ CO ₃ , Bi ₂ O ₃ and Cr ₂ O _{3 in} the above composition range and firing. In this case, the firing temperature is 1300 ~ 1350 ℃
It is preferably within the range.

[Action]

Of BaO-Nd ₂ O ₃ -TiO ₂ based dielectric ceramic composition, BaO · N
By substituting a part of BaO with K ₂ O + Bi ₂ O ₃ in the composition region near d ₂ O ₃ · 5TiO ₂ , the temperature coefficient τ _f decreases and Q _o ≧ 20
00 is achieved.

Further, the addition of Cr ₂ O ₃ lowers the firing temperature and improves the sintered body.

[Examples] Hereinafter, specific examples of the present invention will be described, but the present invention is not limited to these examples.

First, BaCO ₃ , Nd ₂ O ₃ , TiO ₂ , and K ₂ CO with a purity of 99.9% or more.
Raw material powders of ₃ , Bi ₂ O ₃ and Cr ₂ O ₃ were prepared.

Next, each of these raw material powders was weighed so as to have a desired composition, mixed with a ball mill using ethanol as a mixed solvent, and then ethanol was evaporated and removed.

Then, it was pressure molded at a pressure of 1000 kg / cm ² , and the molded body was calcined in the air at 1000 to 1100 ° C. for 3 hours.

This was crushed in a mortar and mixed again with a ball mill using ethanol as a mixed solvent to evaporate and remove ethanol.

After that, pressure molding is performed at a pressure of 1500 kg / cm ² , and 130
Baking in air at 0 to 1350 ° C. for 3 hours.

In accordance with the above-mentioned method, the composition of the raw material powder was changed to prepare dielectric ceramic compositions, and Examples 1 to 8 were obtained. Similarly,
The raw material powders were weighed so that the composition was out of the composition range of the present invention, and dielectric ceramic compositions were produced to give Comparative Examples 1 to 8.

The thus-obtained dielectric ceramic composition was processed into a cylindrical dielectric resonator, and the relative dielectric constant ε _r , temperature coefficient τ _f , and Q of the resonant characteristic, temperature change, and resonator size were used. I asked for _o and. The measurement frequency was about 4 GHz.
The results are shown in the table below.

From this table, in Examples 1 to 8, all of the mole fractions x, y, z of the constituents and the amounts of Cr ₂ O ₃ added were within the ranges described above, and excellent dielectric properties were exhibited. On the other hand, in Comparative Examples 1 to 8, any one of these is out of the range, and therefore it is understood that the required dielectric properties are not satisfied.

〔The invention's effect〕

As is clear from the above description, in the high dielectric constant dielectric ceramic composition for microwaves according to the present invention, the relative dielectric constant ε _r ≧ 80 and the temperature coefficient τ _{f at} a frequency of about 4 GHz.
Each requirement of ≦ ± 50 ppm / ° C. and Q _o ≧ 2000 can be satisfied.

Therefore, by adopting the present invention, the size of the microwave filter can be reduced to about ⅓ in volume without impairing other characteristics, as compared with the case of using the conventional dielectric resonator material.
The size can be reduced as follows. The high dielectric constant dielectric ceramic composition for microwaves according to the present invention is a microwave I
It is also useful as a C substrate, and its area can be reduced to 1/9 or less of that of a conventional alumina substrate.
Further, the high dielectric constant dielectric ceramic composition for microwaves of the present invention is also suitable as a dielectric for devices such as capacitors in the microwave region.

[Brief description of drawings]

Figure 1 shows the relationship between the molar fraction of K ₂ O · Bi ₂ O ₃ and the temperature coefficient τ _f . Figure 2 shows the relationship between the molar fraction of K ₂ O · Bi ₂ O ₃ and Q _o . FIG. 3 is a characteristic diagram showing the relationship between the molar fraction of Nd ₂ O ₃ and temperature coefficient τ _f , and FIG. 4 is a characteristic diagram showing the relationship between the molar fraction of Nd ₂ O ₃ and Q _o . is there. Fig. 5 is a characteristic diagram showing the relationship between the firing temperature with and without addition of Cr ₂ O ₃ and the density ρ of the resulting dielectric ceramic composition, and Fig. 6 is the amount of Cr ₂ O ₃ added and the temperature coefficient. FIG. 7 is a characteristic diagram showing the relationship between τ _f and FIG. 7 is a characteristic diagram showing the relationship between the amount of Cr ₂ O ₃ added and Q _o .

Claims (1)

[Claims] 1. A general formula xBaO · y (K ₂ O · Bi ₂ O ₃ ) · zNd ₂ O ₃ · (6-z) TiO ₂ whose composition range is 0.88 ≦ x ≦ 0.98 0.056 ≦ y ≦ A high-dielectric-constant dielectric ceramic composition for microwaves, which comprises, as a main component, a composition satisfying 0.110 0.95 ≦ z ≦ 1.11 and 0.5% by weight or less of Cr ₂ O ₃ as an accessory component.