JP3311928B2 - Alumina sintered body for high frequency - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a dielectric resonator, a high-frequency waveguide, a high-frequency capacitor, a high-frequency IC substrate, and an IC.
The present invention relates to an alumina-based sintered body suitably used for high-frequency applications in the field of telecommunications such as packages and dielectric antennas or in the field of nuclear fusion-related equipment such as microwave transmission windows.

[0002]

2. Description of the Related Art In recent years, with the development of communication networks, operating frequencies have been increasing to high frequency ranges such as microwave and millimeter wave ranges. In these high-frequency regions, dielectric porcelain is applied to resonators, integrated circuit boards, antennas, impedance matching of various high-frequency circuits, and the like. In particular, it is required for stabilizing the frequency of a filter, a gun, or an FET microwave oscillator, and the demand thereof is increasing.

The characteristics of a microwave dielectric material include:
It is necessary that the Q value (= 1 / tan δ) is large and the temperature coefficient (τf) of the resonance frequency can be controlled. In addition, a material having a large relative dielectric constant has been conventionally developed for downsizing the device. However, as the operating frequency increases, it is considered that a material having a small relative dielectric constant is also desired from the viewpoint of workability.

Until now, the alumina-based sintered body most frequently used as a ceramic material is obtained by adding SiO ₂ , CaO, MgO, or the like as a sintering aid to alumina and sintering it. but this alumina sintered body, as small as 10 dielectric constant than the microwave dielectric materials, such as a conventional BaO-TiO ₂ system. In addition, single crystal Al
_{Since 2} O ₃ has a very high Q value, the original Q value of Al ₂ O ₃ is high, and it is considered that Al ₂ O ₃ has high performance as a high-frequency dielectric material. Furthermore, the alumina-based sintered body
It has the advantages of excellent mechanical strength, thermal conductivity and chemical stability, and low cost.

[0005]

However, the conventional alumina sintered body has a large temperature coefficient (.tau.f) of the resonance frequency of -60 ppm / .degree. As a result, its use has been severely restricted. In addition, the Q value is greatly reduced by impurities in the alumina raw material powder and additives such as a sintering aid, and at present, excellent characteristics inherent in the powder cannot be obtained.

As a method of adjusting the temperature coefficient τf of the resonance frequency to around ± 0, a method of combining substances having different signs of τf is known. In that case, the Q value of the complex is
It is governed by the Q value of the substance to be combined. Therefore, as a substance to be compounded with alumina having a large negative τf,
It is desirable that τf be a positive and large value and have a high Q value. Therefore, TiO ₂ is noted as a substance having a large positive τf and a high Q value. However, when TiO ₂ is added to Al ₂ O ₃ and sintering is performed, Al ₂ TiO ₅ is usually generated, so that the desired characteristics cannot be obtained. In order to suppress the formation of Al ₂ TiO ₅ , the third addition is performed. I needed something.

Accordingly, the present invention has a high Q value containing alumina as a main component, and has a temperature coefficient τf of the resonance frequency.
It is an object of the present invention to provide a novel material capable of reducing the absolute value of

[0008]

Means for Solving the Problems The present inventors have proposed Al ₂ O
As a result of further study on _3- TiO ₂ material,
Even when the third additive was not added, if the firing temperature was set low, it was found that the reaction for producing Al ₂ TiO ₅ did not proceed. The Al ₂ O thus obtained is
_The present inventors have found that, if the _3- TiO ₂ composite material is dense, τf is small and has a higher Q value, and the present invention has been achieved.

[0009] That is, the high frequency alumina sintered body of the present invention is composed of a 78 to 96% by volume in terms of oxide of Al, and 4 to 22 vol% in terms of oxide of Ti, Al ₂ O ₃ ( It contains a corundum) crystal phase as a main phase, a TiO ₂ (rutile) phase at a ratio of 4 to 14% by volume, an open porosity of 3% or less, and a dielectric loss (t) at a measurement frequency of 10 GHz.
an δ) is 5 × 10 ⁻⁴ or less and the resonance frequency is 25 to 85 ° C.
The absolute value | τf | of the temperature coefficient at 30 ppm / ° C. or less.

[0010]

The τf of alumina is a large negative value of −60 ppm / ° C. Therefore, in order to reduce the absolute value of τf of alumina, Ti in which the τf is +440 ppm / ° C.
It is effective to make the O ₂ phase coexist. On the other hand, Al ₂ T
iO ₅ phase is a substance produced as sintering a mixture of Al ₂ O ₃ and TiO ₂ at a high temperature, the Al ₂ TiO
_{Even if the five} phases coexist with the Al ₂ O ₃ phase, the absolute value of τf cannot be reduced. Therefore, in the present invention, Al ₂ O
It is necessary to stably coexist the TiO ₂ phase in the sintered body in addition to the _three phases. In the Al ₂ O ₃ —TiO ₂ system, Al ₂ TiO ₅ becomes a stable phase at a high temperature (1200 ° C. or higher), so that almost no TiO ₂ phase remains.
The TiO ₂ phase can be stably present together with the l ₂ O ₃ phase.

Therefore, in the present invention, Al ₂ O ₃ —TiO
_{The two} -component composition is fired at a relatively low temperature, and TiO ₂ (rutile) is added to the main phase composed of Al ₂ O ₃ (corundum).
The phases can coexist at a rate of 4 to 14% by volume, and by making the open porosity 3% or less, the absolute value of the temperature coefficient τf of the resonance frequency in a high frequency or microwave region is reduced. A sintered body having a high Q value can be obtained.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The alumina-based sintered body of the present invention comprises A
The main phase is an l ₂ O ₃ (corundum) phase, and at least a TiO ₂ (rutile) phase is included as another crystal phase. According to the present invention, the Al ₂ O ₃ phase in the sintered body in which a main phase, TiO ₂ phase 4-14% by volume, to be present in a proportion of particularly 7-11% by volume is important. This is because when the TiO ₂ phase is less than 4% by volume, τf is −3.
Less than 0 ppm / ° C and 14% by volume of TiO ₂ phase
If it is larger, τf becomes larger than +30 ppm / ° C. In the sintered body of the present invention, an Al ₂ TiO ₅ phase may be present in addition to the Al ₂ O ₃ phase and the TiO ₂ phase, but the Al ₂ TiO ₅ phase is different from the TiO ₂ phase. It does not have the effect of controlling the τf of alumina and, if present in a large amount in the sintered body, increases the dielectric loss.
The smaller the amount of the l ₂ TiO ₅ phase, the better.
It is desirable that the content be not more than% by volume. Further, there may be a case where a glass phase composed of these components slightly exists.

According to the alumina-based sintered body of the present invention, since the crystal phase is controlled within the above range, A
1 contains 78 to 96% by volume in terms of oxide, and contains 4 to 22% by volume in terms of oxide in terms of oxide. If these ratios deviate, the ratio of each crystal phase is controlled to the above range. It becomes difficult. It is also important that the alumina-based sintered body of the present invention has an open porosity of 3% or less. This is because if the open porosity exceeds 3%, the dielectric loss in the high frequency region increases.

According to the present invention, the dielectric loss (tan δ) at the measurement frequency of 10 GHz is 5 ×
10 ^-4 or less, especially 2 × 10 ^-4 or less, resonance frequency of 25 to
30 ppm of absolute value | τf | of temperature coefficient at 85 ° C
/ ° C or less can be easily controlled.

In the present invention, in order to produce the above sintered body, first, as a raw material powder, A having a purity of 99.8% or more is used.
An l ₂ O ₃ powder and a TiO ₂ powder having a purity of 99.8% or more are prepared. In particular, according to the present invention, in order to enhance the sinterability at a low temperature, the particle size of the Al ₂ O ₃ powder is preferably small, and particularly, the BET specific surface area of the Al ₂ O ₃ powder is 12 m ^2.
/ G or more.

Then, these powders are mixed with Al ₂ O ₃ powder 7
And 8-96% by volume, were weighed at a ratio of TiO ₂ powder 4 to 22% by volume by adding the organic binder or the like are mixed by a ball mill or the like. At this time, in accordance with the addition amount of TiO ₂ is increased, sinterability, to become high, it is necessary to adjust the amount of TiO ₂ in accordance with the sintering of Al ₂ O ₃ powder used. Then, the mixture is formed into an arbitrary shape by a desired forming means, for example, a die press, a cold isostatic press, an extrusion molding, a doctor blade method, a rolling method, and the like, and then fired.

The firing is performed at a temperature of 1350 ° C. or less, especially 1300 ° C.
Sintering is performed for 1 to 5 hours in an oxidizing atmosphere such as air at the following temperature, and sintering is performed for a time sufficient for the open porosity to be 3% or less, particularly 2% or less. If the firing temperature is higher than 1350 ° C,
An Al ₂ TiO ₅ phase is generated, τf cannot be controlled, and dielectric loss increases. The dielectric loss can be further reduced by lengthening the firing time to promote densification.

[0018]

EXAMPLE As Al ₂ O ₃ powder, purity 99.99
%, BET specific surface area 15 m ² / g, purity 99.8%,
BET specific surface area 8m ² / g, purity 99.9%, BET
Three types having a specific surface area of 7 m ² / g were prepared, and 100 g of the composition shown in Table 1 was prepared using a powder having a purity of 99.9% and a BET specific surface area of 2 m ² / g as a TiO ₂ powder.
300 g of 9% alumina balls (diameter 10 mm) and 100 g of isopropyl alcohol were put into a 500 ml polypot and mixed by a rotary mill for 24 hours. Next, 5 wt% of paraffin wax was mixed, dried and passed through a 40 mesh. 1000 kg / cm
Molded in ² . The firing was performed in the air under the conditions shown in Table 1 to obtain a cylindrical sintered body.

After polishing the obtained cylindrical sample,
The open porosity was measured by the Archimedes method, the crystal phase was identified by X-ray diffraction measurement, and the ratio of each crystal phase to the total crystal phase was determined by the calibration curve method.
The measurement frequency is 10 GHz by the dielectric cylinder resonator method.
To measure the relative dielectric constant (εr) and the dielectric loss (tan δ), and the temperature coefficient τf of the resonance frequency of 25 to 85 ° C.
Was measured. Table 1 shows the results.

[0020]

[Table 1]

According to Table 1, samples Nos. 1, 5, 10, 11, 12, and 12 in which the amount of the TiO ₂ phase precipitated was less than 4% by volume.
In Sample No. 19, | τf | exceeded 30 ppm / ° C., and conversely, even in Samples Nos. 20 and 22, in which the amount of the TiO ₂ phase was more than 14% by volume, the value was too large on the + side. In sample No. 21 having an open porosity of more than 3%, the dielectric loss was 6.
It was as large as 0 × 10 ⁻⁴ .

[0022] In contrast, the samples of the present invention other than the above, any 1500 ° C. to sinter at a temperature of TiO ₂
By precipitating an appropriate amount of the phase, τf is set to −30 to +30.
It can be seen that control can be performed in the range of ppm / ° C. Further, the samples of the present invention all had characteristics of a dielectric loss of 5 × 10 ⁻⁴ or less and a relative dielectric constant of 11 or more.

[0023]

As described in detail above, according to the present invention, A
In l ₂ O ₃ -TiO ₂ based materials, low dielectric loss in a high frequency range, | .tau.f | a can provide a material that can be controlled to below 30 ppm / ° C.. Thereby, the dielectric resonator, the microwave waveguide, the microwave capacitor, and the microwave I
It can be suitably used for high-frequency applications in the field of telecommunications such as C-substrate, IC package, dielectric antenna, etc. or in the field of nuclear fusion related facilities such as microwave transmission windows.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C04B 35/10

Claims (1)

(57) [Claims] (1) Al is 78 to 96% by volume in terms of oxide;
Ti is composed of 4 to 22% by volume in terms of oxide, and Al ₂
It contains an O ₃ (corundum) crystal phase as a main phase, a TiO ₂ (rutile) phase at a rate of 4 to 14% by volume, an open porosity of 3% or less, and a dielectric loss (tan δ) at a measurement frequency of 10 GHz of 5%. × 10 ^-4 or less, 25 of resonance frequency
The absolute value of the temperature coefficient | τf |
m / ° C. or less.