JPH0256305B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to dielectric materials used in microwave circuit elements, microwave circuit boards, etc. The present invention relates to a dielectric ceramic composition having a small temperature coefficient. (Prior Art) In recent years, with advances in microwave circuit technology, circuits have been made smaller. Traditionally, this microwave frequency band (300MHz
Cavity resonators, antennas, etc. have been used in circuits of up to 30 GHz), but these are not suitable for miniaturizing circuits because their size is about the same as the wavelength of microwaves. In contrast, in recent years, microwave filters using dielectric resonators used in the microwave frequency band, small dielectric resonators for stabilizing the frequency of oscillators, capacitors and boards for microwave ICs, etc. Applications have been made to miniaturize circuits by using dielectric ceramics in microwave circuits. The characteristics required of these porcelains are low dielectric loss in the microwave frequency band, high dielectric constant suitable for the frequency band used,
The temperature coefficient of dielectric constant is small. Traditionally, TiO2 _- based materials have been commonly used as porcelain materials that satisfy these characteristics, especially
BaO−TiO ₂ -based porcelain, porcelain in which part of it has been replaced with other elements, and TiO 2 with a negative temperature coefficient and TiO ₂ with a positive temperature coefficient in order to adjust the temperature coefficient of dielectric constant. Many combinations of dielectric materials such as porcelain and glass have been devised and applied. (Problems to be solved by the invention) Conventional TiO ₂ -based, especially BaO-TiO ₂ -based porcelain materials have problems such as not having a sufficiently high dielectric constant, not having a sufficiently small dielectric loss, or not being able to obtain a desired temperature coefficient. It is difficult to stably obtain a material that satisfies all of the properties, such as the absence of carbon dioxide, and there are many practical problems. (Means for Solving the Problems) In view of these drawbacks, the inventors studied various composition systems and found that the main component composition was calcium titanate [CaTiO ₃ ] and lanthanum titanate [La ₂ Ti ₂ O ₇ ], magnesium neodymium titanate [Nd (Mg _1/2 Ti _1/2 ) O ₃ ), and a mixture of magnesium titanate and zinc oxide [MgTiO ₃ 1/2 ZnO], whose main component composition is x [ CaTiO ₃ ]・y
[La ₂ Ti ₂ O ₇ ]・z [Nd (Mg _1/2 Ti _1/2 ) O ₃ ] +w
[MgTiO ₃ 1/2ZnO], when expressed as x + y + z + w = 100 (x, y, z, w are molar ratios),
x, y, z, w are 10≦x≦75, 0<y≦25, 15≦
A dielectric ceramic composition in which z≦75, 5≦w≦40,
It was discovered that this material has excellent properties as a dielectric ceramic for use in dielectric resonators, microwave capacitors, substrates, etc., and is suitable for practical use. (Example) The present invention will be described below with reference to Examples. The starting materials for making the samples are MgO, CaCO ₃ , TiO ₂ , Nd ₂ O ₃ , with a purity of 99.9% or more.
Using La ₂ O ₃ and ZnO powder, CaTiO ₃ and
La ₂ TiO ₇ and Nd (Mg _1/2 Ti _1/2 ) O ₃ and MgTiO ₃・1/2
Each ZnO composition was weighed and put into a ball mill together with pure water for wet mixing. After drying this mixture, the resulting calcined powder was calcined at 800 to 1100℃ for 4 hours, and the resulting calcined powder was mixed to have each predetermined composition, and then put into the ball mill together with pure water again and wet-pulverized. I did it. After drying the pulverized product obtained in this way, a pressure of 1.5 ton/cm ² was applied to the granulated powder obtained by adding and kneading an aqueous binder solution. Firing was performed in air for 2 hours to obtain a fired body. Thereafter, a dielectric resonator was constructed using the obtained ceramic, and the resonant frequency and no-load Q of the dielectric resonator were measured to determine the dielectric constant. The resonant frequency of the obtained dielectric resonator was 4 to 8 GHz. The temperature dependence of the resonant frequency is the temperature change of the resonant frequency of the dielectric resonator from +25℃.
It was determined by measuring between +85°C. Note that the temperature coefficient τf of the resonance frequency is approximately connected to the temperature coefficient τε of the dielectric constant by the following equation. τf=−1/2τε−α Where, τf: Temperature coefficient of resonance frequency τε: Temperature coefficient of dielectric constant α: Coefficient of thermal expansion of porcelain The measurement results for the obtained samples are shown in Table 1. The samples marked with * in this table are comparative examples outside the scope of the present invention, and the other samples are examples within the scope of the present invention. As shown in Table 1, the dielectric ceramic composition of the present invention has a relative dielectric constant of 30 or more, and the temperature coefficient of the dielectric constant is ± over a wide temperature range.
In addition, the Q value, which represents the loss of the dielectric, is kept within the range of 100 ppm/°C at frequencies in the microwave band.
It can be seen that this is a material that can obtain large values of 2000 or more. Further, in the present invention, the reason for limiting the component range is as follows. For [CaTiO ₃ ], Q less than 10 moles becomes low, and more than 75 moles increases the temperature coefficient, and for [La ₂ Ti ₂ O ₇ ],
If it is not included, τf will be large on the negative side, and if it is more than ₂₅ mol, Q will be _low .
For [O ₃ ], if it is less than 15 moles, the temperature coefficient becomes large, and if it is more than 75 moles, Q becomes small, and for [MgTiO ₃ 1/2ZnO], if it is less than 5 moles, a high sintering temperature is required. This is because if the amount exceeds 40 moles, ε becomes low and the temperature coefficient becomes large.

[Table] (Effects of the Invention) As described above, the dielectric ceramic composition according to the present invention has a large dielectric constant of about 50 at microwave frequencies, a small dielectric loss, and a temperature coefficient of the dielectric constant. It can be seen that this is a small material. It is clear that these dielectric ceramic materials are extremely useful as circuit elements and substrates used in the microwave frequency band. It was confirmed that this material has low dielectric loss even in the low frequency range and is an excellent material for capacitors with a high Q value.

Claims (1)

[Claims] 1. The main component composition is calcium titanate [CaTiO ₃ ], lanthanum titanate [La ₂ Ti ₂ O ₇ ], and magnesium neodymium titanate [Nd (Mg _1/2
It consists of a mixture of Ti _1/2 ) O ₃ ), magnesium titanate, and zinc oxide [MgTiO ₃ 1/2ZnO], whose main component composition is x[CaTiO ₃ ]・y[La ₂ Ti ₂ O ₇ ]・z
[Nd (Mg _1/2 Ti _1/2 ) O ₃ ] + w [MgTiO ₃・1/2ZnO],
When expressed as x+y+z+w=100 (x, y, z, w are molar ratios), x, y, z, w are 10≦x
A dielectric ceramic composition for microwave use, characterized in that ≦75, 0<y≦25, 15≦z≦75, and 5≦w≦40.