JPS6350309B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a dielectric ceramic composition suitable for microwave use. In recent years, with the development of microwave integrated circuit (abbreviated as MIC) technology, new fields of application of dielectric materials are being expanded to include dielectric substrates, dielectric resonators, chip capacitors, etc. However, in these fields, existing dielectric materials do not necessarily satisfy the required properties, and research is actively progressing on new dielectric materials for microwaves that can meet the required properties. The current situation is that
In particular, the dielectric materials used in dielectric resonators for microwaves have had few examples of this type of application in the past, and the conditions required for their characteristics are severe, and the characteristics may not be easily met. Research is currently actively underway. The conditions necessary for materials for dielectric resonators are:
(1) The dielectric constant is in the range of 30 to 40, (2) In compensating for the temperature coefficient of stripline, FET, etc.
The temperature coefficient of the dielectric constant can be freely controlled on the order of 10 ^-6 /℃ without significantly changing the relative dielectric constant, and (3) the dielectric loss must be as small as possible (the temperature coefficient of the complex dielectric constant can be controlled at a measurement frequency of 10 to 12 GHz). loss factor
tan δ<5×10 ⁻⁴ : that is, Q>2000). Although it would be ideal to be able to control these individual characteristic values independently, it is difficult to achieve this. However, it is desirable to get as close to that condition as possible. Conventionally, titanate-based porcelain compositions have been mainly studied as this type of dielectric material for microwaves, but titanate-based compositions generally have a large change in specific dielectric constant due to changes in composition; When controlling the temperature coefficient of , the relative dielectric constant may change greatly at the same time, making it impossible to obtain the required value of the relative permittivity, which has the drawback of being subject to limitations. Although it has been greatly improved by the introduction of additives, sufficient characteristics have not yet been achieved. As an example, MgO―
Examples of the CaO-TiO ₂ -Nd ₂ O ₃ system are shown in Table 1 below.

[Table] In this case, the measurement frequency is 2 to 4 GHz.
According to Table 1, it can be seen that the change in relative dielectric constant due to composition change is large. In addition, the relative permittivity and the temperature coefficient of permittivity can be considered to be approximately constant in the microwave range, but
It has been confirmed that tan δ tends to increase as the frequency increases, and is approximately 1.5 to 2 times the above value especially at 10 to 12 GHz. As described above, in conventional compositions, when the temperature coefficient of dielectric constant is changed by changing the composition, the value of relative dielectric constant also changes considerably at the same time. The present invention has been made to overcome the above-mentioned problems, and has a composition represented by (CaxSryBaz)ZrO ₃ (x+y+z=1), 0.88≦x<1 0<y≦0.1 The present invention relates to a dielectric ceramic composition for microwave use, which satisfies 0<z≦0.035 and is fired at a temperature of 1450° C. or higher. The porcelain composition constructed in this way has a relative dielectric constant in the range of approximately 30 to 35 with little change, and also satisfies the condition of tan δ < 5 × 10 ^-4 ,
Therefore, it is suitable as a material for dielectric resonators. Next, the reason why the composition of the ceramic composition according to the present invention is limited to the above range will be explained. First, the reason for setting the Ca content to 0.88≦x<1 is that
This is because if Ca is less than 0.88, tan δ increases too much and the material is not suitable as a dielectric resonator material. In addition, the production range of Sr and Ba is 0<y≦0.1, 0
The reason for setting <z≦0.035 is that if one or both of Ba and Sr is not included, the growth of particles (grains) will be rapid and the size of the grains will be too large compared to the standing wave, resulting in cracks during use. This is because there is a risk that the sintering property may be deteriorated. On the other hand, when the Sr content exceeds 0.1, the sinterability decreases and tan δ becomes larger than 5×10 ^-4 , and when the Ba content exceeds 0.035, the relative dielectric constant changes greatly and This is because the tan δ is also larger than 5×10 ⁻⁴ and the temperature coefficient of the dielectric constant is negative and too large. In either case, it is not preferable as a material for a dielectric resonator. Also, the firing temperature
The reason why the temperature is set at 1450°C or higher is that as the firing temperature becomes lower than 1450°C, tan δ' increases. Next, the present invention will be explained in more detail with reference to examples. Each sample in this example was prepared as follows. First, CaCO ₃ with a purity of 99.99% or more,
Each raw material powder of SrCO ₃ , BaCO ₃ , and ZrO ₂ is prepared.
Next, each of these powders was weighed to have the desired composition, wet-mixed in a ball mill, dried, and pressure-molded at a pressure of about 1000 kg/ ^cm2 .
Bake in air at 1200℃ for about 1 hour. This is ground in a mortar, etc., wet-mixed again in a ball mill,
After drying, it is pressure molded at a pressure of 1000 to 1500 kg/cm ² and fired in air at 1500°C for about 2 hours. The ceramic composition obtained in this way was processed to form a cylindrical dielectric resonator, and its characteristics were measured by the transmission resonance method in combination with a waveguide. From the values and the shape of the resonator, the relative dielectric constant of the sample was determined. tanδ was calculated respectively.
In addition, the temperature of the measurement system was changed, and the temperature change in the dielectric constant was determined from the change in the resonance frequency and the linear expansion coefficient of the material. The measurement frequency was 10 to 11 GHz, and the temperature change range was 20 to 60°C. The results are shown in Table 2 below.

[Table] As can be seen from Table 2, samples No. 1 to 3 satisfy the above-mentioned ranges for x, y, and z, and the firing temperature is as high as 1500°C, so they are suitable for use in dielectric resonators. It fully satisfies the material requirements. That is, the relative dielectric constant is in the range of about 30 to 35, with little variation, and tan δ is also smaller than 5×10 ⁻⁴ . On the other hand, samples No. 4 to 9 have x, y, z
Since any one of these is outside the above-mentioned range, it is found that the material is unsuitable as a material for a dielectric resonator. Describing samples Nos. 4 to 9 in more detail,
In Samples Nos. 4 to 9, the Ba content is outside the range of the present invention, and in Samples Nos. 5 to 9, the Ca composition is also outside the range. In these examples, the change in dielectric constant is relatively large, and tan δ also becomes larger than 5×10 ⁻⁴ . Samples No. 7 and 8 are examples that do not contain either Ba or Sr, but both had poor sinterability and were impossible to measure. Furthermore, other experiments have shown that tan δ is also affected by the firing temperature, and generally tan δ increases as the firing temperature decreases. It was confirmed that the suitable firing temperature for the dielectric resonator material is 1450°C or higher. FIGS. 1 to 3 show the relationship between the composition of the ceramic composition, relative permittivity, temperature coefficient of permittivity, and tan δ, respectively. The region surrounded by thick lines and broken lines represents the composition range according to the present invention. As is clear from these graphs, the ceramic composition according to the present invention satisfies all the conditions necessary for the dielectric resonance material described above, whereas the ceramic composition according to the present invention outside the composition range It can be seen that this material is not suitable as a material for a dielectric resonator, and in particular, the tan δ is considerably larger than 5×10 ⁻⁴ . Note that the ceramic material according to the present invention can of course be applied not only as a material for microwave dielectric resonators, but also for microwave chip capacitors and the like. As explained above, according to the present invention, tanδ
< 5 × 10 ^-4 and then changing the composition and changing the temperature coefficient of permittivity, the change in relative permittivity is significantly smaller than in the conventional example, which is a problem with the conventional technology. can almost be solved.

[Brief explanation of the drawing]

Figure 1 is a composition diagram showing the relationship between the composition and relative permittivity of a porcelain composition, Figure 2 is a composition diagram showing the relationship between the composition and the temperature coefficient of permittivity, and Figure 3 is the relationship between composition and tanδ. FIG.

Claims (1)

[Claims] 1 (CaxSryBaz) A composition represented by ZrO ₃ (however,
x+y+z=1), 0.88≦x<1 0<y≦0.1 0<z≦0.035, and is fired at a temperature of 1450° C. or higher.