JPS6141863B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a high-frequency dielectric ceramic composition composed of barium oxide (BaO), titanium oxide (TiO ₂ ), samarium oxide (Sm ₂ O ₃ ), and aluminum oxide (Al ₂ O ₃ ). , the purpose is to have a large relative dielectric constant (ε _r ),
In the microwave frequency band, the unloaded Q (Q _u ) when used as a dielectric resonator is large, and the temperature coefficient (τ _f ) of the resonant frequency has a stable value, and the temperature coefficient can be varied over a wide range depending on the application. The object of the present invention is to provide a dielectric ceramic that can be changed. In recent years, with advances in technology for high-frequency circuits that handle microwaves and millimeter waves (hereinafter referred to collectively as microwaves) with wavelengths of several centimeters or less, efforts are being made to miniaturize these circuits. . Until now, this high-frequency circuit used cavity resonators,
Antennas have been used, but their size is comparable to the wavelength of microwaves, which has been an obstacle to miniaturization. In order to solve this problem, a method has been taken to shorten the wavelength itself by using dielectric ceramics with a high dielectric constant. Materials suitable for this kind of use are
TiO ₂ -based materials are often used, such as TiO ₂ −
ZrO ₂ −SnO ₂ system, CaTiO ₃ −MgTiO ₃ −La ₂ O ₃ −
2TiO ₂ series, recently Ba(Zn _1/3 Ta _2/3 )O ₃ −Ba
Dielectric ceramics such as (Zn _1/3 Nb _2/3 )O ₃ are known. However, when making a dielectric resonator using these materials, the dielectric constant is as low as about 30, so for example, a material with ε _r = 30 is used for an X-band dielectric resonator with a resonance frequency of about 11 GHz. In this case, the unit will be small with a diameter of 5.6 mm and a thickness of about 2.2 mm, but if the frequency is lowered and it is used in the UHF band of about 2 GHz, the diameter will be reduced for the same material with ε _r = 30.
The size is significantly larger at 30.7mm and the thickness is about 12.3mm. If the dielectric constant of the material used here can be increased to around 80, the size will be 18.8 mm in diameter,
Although it can be made smaller with a thickness of approximately 7.5 mm, it has not been possible to satisfy such requirements with conventional materials. The present invention has been made to improve these drawbacks, and has improved relative dielectric constant and no-load Q, has a stable temperature coefficient of resonance frequency, and can vary this temperature coefficient over a wide range depending on the application. The object of the present invention is to provide dielectric ceramics that can be used in various ways. As a result of various studies on materials that meet the above requirements, the inventors found that in the composition represented by xBaO−yTiO ₂ −zSm ₂ O ₃ , 5≦x≦ in molar percentage.
23, 57≦y≦82.5, 2.5≦z≦37.5, x+y+z=
It has been found that porcelain having a composition in which Al ₂ O ₃ is added in an amount not exceeding 3% by weight with respect to the main components in the range of 100 is an excellent dielectric porcelain for high frequency use. The reason for limiting the range of the main component composition is that the amount of BaO (x) is more than 23 mol% or
This is because if the amount of TiO ₂ (y) is less than 57 mol% or the amount of Sm ₂ O ₃ (z) is less than 25 mol%, it becomes difficult to sinter the porcelain, and the no-load Q decreases, making it impossible to measure. . In addition, x is less than 5 mol% or z is
If it exceeds 37.5 mol%, the sintering of the porcelain becomes unstable and the no-load Q decreases, making it impossible to measure.If y exceeds 82.5 mol%, the sintering of the porcelain becomes unstable and However, since the change in temperature characteristics becomes significantly large, it is excluded from the scope of the present invention. Furthermore, with regard to the addition of Al ₂ O ₃ as a subcomponent, as the amount added increases, the no-load Q can be increased and the temperature characteristics can be changed;
When added in an amount exceeding 3% by weight, sintering becomes unstable and the no-load Q decreases, so it is excluded from the scope of the present invention. The present invention will be explained below based on examples. Starting materials include chemically highly purified BaCO ₃ ,
TiO ₂ , Sm ₂ O ₃ and Al ₂ O ₃ were weighed to give a predetermined composition and wet-mixed with pure water in a rubber-lined ball mill equipped with an agate ball. This mixture was taken out from the ball mill, dried, and then calcined in air at a temperature of 900° C. for 2 hours. The calcined product was wet-milled together with pure water in the ball mill described above. After dehydrating and drying the crushed slurry, 8% by weight of a 3% concentration polyvinyl alcohol solution was added to the powder as a binder to make it homogeneous.
The grains were sized through a 32 mesh sieve. The sized powder was molded into a disk with a diameter of 20 mm and a thickness of about 8 mm using a mold and a hydraulic press at a molding pressure of 800 kg/cm ² . The molded body is placed in a high-purity alumina pot and heated in air at a temperature ranging from 1250℃ to 1550℃ depending on the composition.
The mixture was held for 2 hours and fired to obtain dielectric porcelain having the composition shown in the table. Using this ceramic element, the resonant frequency, no-load Q, and relative dielectric constant were determined from measurements using the dielectric resonator method. The temperature dependence of the resonant frequency is −30
The temperature coefficient τ _f was determined by measuring in the range from ℃ to 70℃. The resonant frequency was between 2 and 4 GHz. The experimental results are shown in the table. Note that the samples marked with * in the table are comparative examples outside the scope of the present invention, and the other samples are examples within the scope of the present invention.

【table】

[Table] As is clear from the table, in the dielectric ceramic within the scope of the present invention, the no-load Q can be increased while keeping the relative dielectric constant high. Furthermore, since the dielectric ceramic of the present invention exhibits stable temperature characteristics, it is useful for stabilizing the temperature dependence of oscillators and resonators.
Suitable for use in the UEF band, it is possible to create small, high-performance electronic circuit components. Furthermore, since the value of τ _f can be selected within a wide range by changing the material composition, when the dielectric resonator is assembled, it can have a temperature compensation effect that eliminates the influence of the surrounding metal plates on the temperature characteristics. I can do it. Furthermore, the dielectric ceramic composition of the present invention can provide a material useful not only for dielectric resonators but also for microwave substrates, dielectric adjustment rods, etc., and has great industrial utility value. It is.

Claims (1)

[Claims] 1 Dielectric porcelain made of barium oxide, titanium oxide, samarium oxide, and aluminum oxide, whose main component composition formula is expressed as xBaO−yTiO ₂ −zSm ₂ O ₃ , where x, y, and z are 5≦ in mole percentage. x≦23,
57≦y≦82.5, 2.5≦z≦37.5, x+y+z=100
1. A dielectric ceramic composition characterized in that Al ₂ O ₃ is added in an amount not exceeding 3% by weight based on the main component.