JPS5918806B2 - Ceramic composition of dielectric resonator for microwave band - Google Patents

Description

Detailed Description of the Invention The present invention has an excellent temperature coefficient of dielectric constant in microwaves, particularly in the 4 to 12 GHz band, and a low dielectric loss (tan δ
) relates to a ceramic composition for an extremely small dielectric resonator for the microwave band.

Circuit elements using dielectric resonators are becoming increasingly popular as a means for downsizing microwave circuits or for frequency stabilization.

For such applications, the electrical properties required for dielectric ceramics are a large no-load Q (Qu), in other words, a small dielectric loss (tan δ), and a small temperature change in the resonant frequency. Therefore, the temperature dependence of the dielectric constant ε must be made small, and the size of ε, which affects the size of the resonator, must be appropriate, and these characteristics must be satisfied at the same time.

Several dielectric materials have been known to meet such severe conditions, but it has been impossible for any of them to simultaneously satisfy the above characteristics.

Therefore, several types of by-products are included in the form of mixed crystals,
Attempts are being made to synthesize multi-component materials and improve them. Ba2Ti002O, Ba-TiO2-Zr
O2 system or (S", Ca) (Lil/hNb3/
hTiX)O2, (Ba, Br, Ca) (TiZr)O
An example is s. However, in these dielectric compositions, the Qu value has frequency dependence, and its deterioration is significant in the λ-band (8 to 12 GHz), so it cannot necessarily be satisfied in that frequency band. It wasn't.

On the other hand, in terms of manufacturing technology, since it is made up of multiple components, precision is required in terms of composition ratio control or sintering conditions, making it difficult to produce industrially. The present inventors have studied in detail the properties of various oxides and titanates in the microwave band, and have created a ceramic composition with a large Qu value even at that frequency by simultaneously maintaining the necessary properties. It is a new discovery.

In other words, magnesium titanate (MgTiO3) has a small ε but a positive temperature coefficient of ε (εTC) and a large Qu value.
In combination with titanium oxide (TiO2), which has a negative εTC but a large ε and Qu value, calcium titanate (CaTiO3), which alone has a negative εTC and a low Qu value, is used as a base composition. By adding and existing it, sintering is promoted and a ceramic composition for a dielectric resonator having excellent characteristics in the microwave band can be obtained.
This excellent effect is obtained by forming a well-balanced mixed crystal of the three components, and the composition range is as follows:
CaTiO3 is added in an amount of 1 to 9% by weight based on a base composition in which MgTlO3 is 70 m01% or more and TiO is 30 (auto)1% or less. Hereinafter, the present invention will be explained based on examples. The example original paper contains reagent-grade purity magnesium oxide, titanium oxide,
Calcium carbonate was used.

First, in order to obtain MgTiO3 and CaTiO, predetermined amounts of raw materials were weighed and wet mixed, and after drying,
℃~1200℃, fired in air for 3 hours, powdered Mg
TiO3 and CaTiO3 were obtained. On the other hand, TiO2 was also used as the titanium oxide. These samples are wet-pulverized again to a predetermined ratio, dried, and then a suitable amount of binder for dry molding is added, and then granulated, and then molded into dimensional shapes. The sample is selected to have a uniform grain size, and the granular sample is inserted into a mold of a hydraulic press machine, and then subjected to 600 to 8,000 kν erosion by the upper and lower molds of the hydraulic press machine. The samples were molded by applying a predetermined pressure depending on the shape in a range of about 2, and sintered in an oxygen atmosphere at 1250 DEG C. to 1400 DEG C. for 5 hours.

Measuring the characteristics of a dielectric resonator in the microwave band is 2
This was carried out using the TEOl mode of a resonator consisting of a cylindrical sample sandwiched between two parallel metal plates.

The temperature coefficient of dielectric constant εTC was measured between -30°C and +70°C. Table 1 shows the characteristic values when the composition ratio of MgTlO3 and TiO2 is changed.

If MgTiO3 does not reach 70m01%, εTC is negative, and the addition of CaTiO causes it to move further to the negative side, which is not preferable. MgTlO3 is 70m01% or more, TiO2 is 30m01 (L or less, εTC is positive and the Qu value is strong. MgTlO3 is 70m01% or more, TiO2 is 30m01 or less.
Table 2 shows the characteristics when a small amount of CaTiO3 is added when O, is 30m01% or less. The amount of CaTiO3 added is MgTlO3 and T! If it does not reach 1% by weight for the composition based on 02, ε is too low, and furthermore, ε
The improvement effect of TC is also not significant. Similarly, if it exceeds 9% by weight, εTC will largely shift to the negative side, and the Qu value will also deteriorate. In addition, Table 2 shows MgTlO39OmOl%, TlO2
The case of a composition based on 1OmOl% is shown.

FIG. 1 shows the effect of adding CaTiO3 on sinterability.

As is clear from FIG. 1, the addition of a small amount of CaTiO3 improves the sintered density and allows the sintering temperature to be lowered. FIG. 2 is a graph showing frequency characteristics in the microwave band of a conventional dielectric composition and a ceramic composition for a dielectric resonator according to the present invention.

(1) is a conventional Ba-TlO2-ZrO2 system, (2) is a conventional Ba2Ti9O2O, and (3) is sample 10 of the present invention. As described above, the dielectric ceramic composition of the present invention can obtain a dielectric constant ε of about 18 to 22 in the microwave band, and the temperature coefficient of the dielectric constant is within a range of about ±50 pprr1/℃ over a wide temperature range. It can be done. Furthermore, the Qu value is 10,000 or more (Tan δ: 1
x10-4 or less), and has an excellent effect particularly for use in the microwave band (X-band). Especially MgTlO39
In a composition in which 6.2% by weight of CaTiO is added to a composition based on OmOl%, TlO2lOmOl%, ε = 20, Qu = 10000 (
It shows an excellent effect with Tan-1×10-4)εTC=0.9 ppm/°C. As described above, in the present invention, the Qu value is extremely high in the microwave band, and the temperature coefficient of dielectric constant is extremely small, so that the microwave circuit can be miniaturized or the resonance frequency can be stabilized.

In particular, excellent performance can be obtained when used in dielectric resonators. For example, microwave local oscillator devices require strict frequency safety, so 12 GH
In the z-band, this cannot be achieved without the ceramic composition for a dielectric resonator of the present invention. Furthermore, it has been fully recognized that a humidity sensor using a microwave dielectric resonator has good sensitivity because Qu is always high, and also has excellent reproducibility.

The mode of the dielectric resonator of the present invention is the TEO of the above embodiment,
In addition to the HOl mode, TEM mode, or those in which the distribution of electric and magnetic fields approximates the above, it is possible to expect the same effect in operation as a dielectric resonator in each applied mode. . Furthermore, even if the dielectric resonator of the present invention is installed in a waveguide or the like and used in a line for propagating microwaves, the gain is sufficiently improved, and the gain is sufficiently improved. Even down to the equipment, it is possible to prevent the heat generation temperature rise of each device as much as possible, etc.
The field of application in microwave band communication equipment has become extremely wide. As described above, the ceramic composition for dielectric resonators having the composition range of the present invention has excellent properties particularly for use in the microwave band (X-pat), and is an industrially useful invention.

[Brief explanation of drawings]

FIG. 1 is a graph showing the effect of adding CaTiO3 of the present invention.

Claims (1)

[Claims] 1. A microwave band comprising 1 to 9% by weight of calcium titanate CaTiO_3 added to a composition consisting of 70 mol% or more of magnesium titanate in terms of MgTiO_3 and 30 mol% or less of titanium oxide in terms of TiO_2. Porcelain compositions for dielectric resonators.