KR100234011B1 - Dielectric ceramic composition - Google Patents

Abstract

In the dielectric ceramic composition for microwave, the dielectric ceramic is composed of a perovskite solid solution mainly composed of CaTiO ₃ , La (Zn _1/2 Ti _1/2 ) O _3, and NdAIO ₃ , and the dielectric constant is large, resulting in small dielectric loss. It is possible to provide an excellent microwave dielectric ceramic having excellent Q × f ₀ (GHz) characteristics and a temperature coefficient of resonant frequency of ± 10 ppm / ° C or less. On the other hand, by finely adjusting the content of CaTiO ₃ , under the same manufacturing conditions it is possible to freely control the temperature coefficient of the resonant frequency centered around 0 ppm / ℃ to + and-.

Description

High Frequency Dielectric Ceramic Composition

The present invention relates to a dielectric ceramic composition for microwaves with low loss and good temperature coefficient of resonance frequency.

Recently, with the advancement of the information society, communication systems using microwaves (frequency band: 300MHz-300GHz) in mobile communication, satellite broadcasting, and satellite communication fields such as wireless telephones and automobile telephones have been remarkably developed. BACKGROUND OF THE INVENTION The application of high frequency dielectric ceramics to resonators, bandpass (or stop) filters, microwave integrated circuits (MIC), and the like has been greatly increased. Until now, many studies have been conducted to develop ceramics that satisfy these conditions. Representative microwave dielectric ceramic materials have a dielectric constant of 20 to 30 years and have high Q (Q × f ₀ = 100000). The composite perovskite solid solution (BMT, BZT, etc.), the dielectric constant is 30-40, the simple solid solution (BT ₄ , BT _9, etc.) having a moderate Q value (Q × f ₀ = 30000), and the dielectric constant Mixed phase materials (BPNT, PCZ, etc.) that have a height of 90-100 but a relatively low Q (Q x f ₀ = 4500).

Important characteristics required for such high frequency dielectric ceramic materials include

V) have a high relative dielectric constant corresponding to the frequency used;

Ii) The Q value is large.

온도계) The temperature coefficient of resonant frequency is close to 0 ppm / ℃.

Viii) It is physicochemically stable and the change over time is small.

I) The mechanical strength and thermal conductivity are large, the thermal diffusivity is good, and the coefficient of thermal expansion is small.

In general, materials with high dielectric constants have low dielectric losses due to defects with dipoles in the dielectric and can be used only when the temperature coefficient of the resonance frequency is stable at about ± 30 ppm / ℃. In the case of CaTiO ₃ , the dielectric constant is very high at 170 GHz at ₃ GHz, but the temperature coefficient of the resonance frequency is about +800 ppm / ℃, which is very large. In the case of La (Zn _1/2 Ti _1/2 ) O ₃ , the dielectric constant is high. Is low as 34, but Q × f ₀ (GHz) is very high as 60000 and the temperature coefficient of resonant frequency is about -60 ppm / ℃. Therefore, the present invention improves the problems of these two materials, the dielectric constant is more than 40, the dielectric loss is small and the temperature coefficient of the resonant frequency can be easily moved to + and-as needed around 0 ppm / ℃ as needed It is intended to provide a composition.

1 is a composition state diagram showing the composition range of the dielectric ceramic composition according to the present invention.

The dielectric ceramic composition for microwaves according to the present invention is a perovskite solid solution mainly composed of CaTiO ₃ , La (Zn _1/2 Ti _1/2 ) O _3, and NdAIO ₃ . As shown in The reason for limiting the range is that the temperature coefficient of the resonant frequency of the dielectric material by these compositions is approximately +80--50 ppm / ° C, so by itself or by adding a small amount of additives, the dielectric loss is small and the temperature characteristics are good for the microwave. It is because a dielectric ceramic can be manufactured.

It will be described in detail through the embodiments of the present invention.

EXAMPLE

The raw material powder was calibrated with each raw material exactly to the composition shown in Table 1 using CaTiO ₃ , La ₂ O ₃ , Al ₂ O ₃ , TiO ₂ , Nd ₂ O ₃ and ZnO having a purity of 99.9%. Mixed. The mixed powder was calcined at a temperature of 1250 ° C. for about 4 hours to synthesize a solid solution having a perovskite structure.

The synthetic powder was pulverized well, press-molded into a disc-shaped specimen having a diameter of 15 mm and a thickness of 6-7 mm, and sintered at a temperature of 1450-1550 ° C. for 2-6 hours. After sintering, the shrinkage of the specimen was about 15-20%.

Both surfaces of the sintered specimens were polished well using abrasive paper (up to # 3000), and then the dielectric constant, Q value, and temperature coefficient of the resonance frequency were measured by dielectric dielectric method. At this time, the measurement frequency was 4-6GHz and the measurement temperature range was -30 ° C to 80 ° C. Microwave dielectric properties of the specimens for each composition are shown in Table 1.

As shown in Table 1, the high frequency dielectric properties did not change significantly depending on the amount of La (Zn _1/2 Ti _1/2 ) O ₃ and NdAlO ₃ , but the properties changed significantly depending on the amount of CaTiO ₃ . . As the CaTiO ₃ content increases, the dielectric constant gradually increases in the range of 40-70 but Q x f ₀ (GHz) decreases and the temperature coefficient of the resonant frequency changes gradually from-to +. Accordingly, excellent dielectric ceramics for microwaves having excellent dielectric constant and Q x f ₀ (GHz) characteristics and a resonant frequency temperature of less than ± 10 ppm / ° C can be produced at around 0.5-0.6 mol of CaTiO ₃ . On the other hand, by finely adjusting the content of CaTiO ₃ , under the same manufacturing conditions it is possible to freely control the temperature coefficient of the resonant frequency centered around 0 ppm / ℃ to + and-.

Microwave dielectric ceramic composition according to the present invention is a perovskite solid solution mainly composed of CaTiO ₃ and La (Zn _1/2 Ti _1/2 ) O ₃ and NdAlO _3, which has a low dielectric loss and a temperature coefficient of resonant frequency of 0 ppm. It is possible to provide a novel dielectric ceramic composition for microwaves that can be easily moved as needed towards + and-centered at / ° C.

Claims (2)

In the composition system represented by general formula (1-x) CaTiO ₃ -x [(1-y) La (Zn _1/2 Ti _1/2 ) O ₃ -NdAlO ₃ ], the ranges of x and y are each 0.2≤x <0.5 and 0 <y <1, the dielectric ceramic composition for high frequency. The dielectric ceramic composition for high frequency as claimed in claim 1, wherein the range of x is 0.4 ≦ x ≦ 0.5.

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