KR970005885B1 - Microwave dielectric ceramics - Google Patents

Abstract

A ceramic composition useful as the raw material for industrial and domestic microwave parts, laminated ceramic capacitor and temperature compensating element of electromagnetic interference filter exhibits a high dielectric constant, low temperature constant of resonance frequency, and good quality factor. The ceramic composition consists of barium oxide, lead oxide, samarium oxide, and titanium oxide as the main components having a composition formula x(BaO1- M,PbO M)-ySm2O3-zTiO2, where x is 6-20, y is 6-20, z is 60-75, M is 0-0.2, and x+y+z is 100.

Description

[Name of invention]

Dielectric Ceramic Composition for Microwave

[Detailed Description of Occurrence]

(Field of invention)

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to ceramic ancestors useful as temperature compensation materials for microwave band components and multilayer ceramic capacitors and electromagnetic interference (EMI) filters used in consumer and industrial electronic devices. The present invention relates to a ceramic dielectric composition having a high temperature coefficient, a low resonant frequency, and a good quality factor (Q).

(Conventional technology)

Recently, as communication means such as automobile telephone, cellular phone, cordless telephone and satellite broadcasting receiver have been widely used, microwave band filter, substrate voltage controlled oscillator (VCO) has been developed due to the development of microwave circuit and integrated circuit. Dielectric ceramics are widely used. Such microwave dielectric ceramics are mainly used as resonators, and the ceramic compositions used herein include BaO-Nd ₂ O ₃ -TiO ₂ , BaO-Sm ₂ O ₃ -TiO ₂ , PbO-ZrO ₂ -CaO Various dielectrics are used. Among BaO-Nd ₂ O ₃ -TiO ₂ and BaO- Sm ₂ O ₃ -TiO ₂ ceramics, the dielectric constant is about 60-80, the quality factor is about 1㎓ to 5000, and the change of temperature coefficient (T _f ) of resonance frequency It is very large and has a big practical problem. In addition, the PbO-ZrO ₂ -CaO system proposed in Japan has a high dielectric constant of more than 90, while the quality factor is low from 1000 to 3500 at high frequencies, and the loss is high at high frequencies of 3 kHz or higher, so the band pass filter (BPF) and voltage There is a disadvantage in that the parts loss such as the adjustable oscillator is increased. The required characteristics to be applied to these parts should be high quality factors (e.g. more than 5000 at 1 kHz) and low temperature stability of the resonance frequency. As a ceramic composition having an improved quality factor, a BaO-Nd ₂ O ₃ -TiO ₂ composition has been proposed in Japan, which reports an improvement in permittivity due to the addition of PbO. The dielectric constant of this system is 88, and the quality factor is reported as 4000-5500. However, PbO is added to increase the dielectric constant, but the composition ratio is 0.5BaO-0.5PbO -1, ONd ₂ O _3-5 TiO ₂ , which has a high composition ratio of lead oxide, and an excessive amount of lead oxide and bismuth oxide in the manufacturing process. Due to the volatilization of these additive elements, uniform composition control is difficult, and these additives are known as very harmful elements to the human body in the manufacturing process, and expensive dielectric oxide is essential dielectric. The conditions required for use in microwave components are that the dielectric constant of the dielectric should be high at high frequencies, the quality factor should be more than 5000, and the temperature coefficient of the resonance wave should be as low as ± 5 ppm / ° C. In addition to satisfying these dielectric properties, the conditions required in the manufacturing process are to prevent quality deterioration by preventing the control of composition by volatilization of the component elements, and the amount of lead and bismuth component elements that are harmful to the human body in the manufacturing process. It is to stably control the manufacturing composition components by reducing the.

(Purpose of invention)

The present invention has been made in view of the above-described conditions, using a sintering aid that is less volatile and harmless to a human body than a conventional dielectric, the composition ratio of the manufacturing element is stabilized and can be manufactured at low manufacturing cost, and the dielectric constant is large and the quality factor is high at high frequency. The purpose is to provide a high microwave dielectric ceramic composition.

Composition of the Invention

According to the present invention, a ceramic dielectric composition useful for microwaves has been obtained through experiments as a dielectric ceramic composition composed mainly of barium oxide, lead oxide, samarium oxide, and titanium dioxide. For example, the present invention provides 60.0-75.0 mol% TiO ₂ as the first component, 6-20 mol% Sm ₂ O ₃ as the second component, and 6-20 mol% BaO _1-a PbOa as the third component. It consists of. The present invention uses samarium oxide, which is cheaper than niobium oxide, to obtain a composition having the same dielectric constant and increased quality factor. In addition, by using the lead oxide of about 3 mol% can prevent the degradation of the quality factor due to the volatilization of the lead component and easy to control the composition.

The dielectric ceramic of the present invention prepared by sintering the composition at a sintering temperature in the range of 1225 ° C. to 1450 ° C. has a dielectric constant of 85 or more and a resonant frequency temperature coefficient within ± 5 ppm / ° C., and a quality of 6000 or more at 1 GHz resonant frequency. Has a coefficient.

Example

Hereinafter, an example of implementing the present invention will be described.

X (BaO _1-a PbO _a ) -ySm ₂ O ₃ -zTiO ₂ composition containing barium oxide, lead oxide, samarium oxide, and titanium dioxide as a main component, are weighed as shown in Table 1, and mixed with deionized water. do. In this case, instead of the barium oxide, barium carbonate (BaCO ₃ ) may be used, and lead trioxide (Pb ₃ O ₄ ) may be used instead of lead oxide (PbO). The mixture uses a ball milling method, using zirconia balls and plastic jars. The dried powder is calcined at 1000 ° C. or higher for 2 hours, and an appropriate amount of polyvinyl alcohol is added and mixed in zirconia induction.

The mixed material is molded into a cylindrical specimen of diameter 10 mm or more and height 5 mm or more using a mold and a hydraulic press. The pressure during molding is 1.0 ton / cm 2 or more. Specimens during molding are sintered using an electric furnace on a zirconia setter at a high temperature above 1200 ° C. in the air atmosphere, that is, the sintering conditions shown in Table 1. The sintered specimens were measured for dielectric constant at about 3 으로 by the Hockey-Colman method, and the no-load Q of the dielectric material was measured by the open resonant method. The temperature coefficient of the resonance frequency was obtained for the temperature range of 25 ° C to 125 ° C by the following equation (1).

F (152) = resonance frequency at 15 ℃

F (25) = resonant frequency at 25 ° C

ΔT = measured temperature difference, in this case 125-(25) = 100

As a result of measuring the dielectric properties of each ceramic dielectric fabricated by the above method, the optimum sintering temperature is decreased and the quality factor is increased as the amount z of titanium dioxide (TiO ₂ ) is increased in the composition. However, when the titanium dioxide is more than 75 mol%, the temperature coefficient of the resonant frequency is shifted positively, which is difficult in practical use. In addition, if it is 60 mol% or less, a chemical composition ratio is not suitable and a dielectric will not be formed. Therefore, it can be seen that the preferred amount of addition (z) of TiO ₂ in the embodiment of the present invention is about 60 to 75 mol%. As the amount of samarium oxide in the composition is increased, the quality factor can be increased, but the optimum sintering temperature is increased to 1400 ° C. or higher, and the temperature coefficient of the resonance frequency is shifted to a positive amount at 18 mol% or more. If the amount is less than 5 mol%, the resonance frequency temperature coefficient is shifted to the positive amount due to the increase in the amount of titanium dioxide added. Therefore, the preferable composition ratio of the samarium oxide component is about 6-20 mol%. As the lead oxide is increased during the composition, the proper sintering temperature is lowered and the dielectric constant is increased. However, when 15 mol% or more is added, it is difficult to control the composition due to volatilization of the lead oxide and the quality factor is lowered. In addition, if the amount of barium oxide in the composition is increased, the quality factor is lowered, but the temperature stability of the resonance frequency can be obtained. In addition, even when barium carbonate (BaCO ₃ ) is used instead of barium oxide (BaO) in the composition, there is no significant change in dielectric properties, and when lead trioxide (Pb ₃ O ₄ ) is used instead of lead oxide (PbO), it is uniform. Mixing occurs and does not significantly affect the dielectric properties.

In the same composition, when the sintering temperature is increased, the dielectric constant and quality coefficient are slightly higher, and when the sintering time is longer, the dielectric constant is almost unchanged, but the quality coefficient is slightly higher. Table 1 summarizes the dielectric properties of each sample prepared under different composition ratios and sintering conditions.

(x + y + z = 100)

(Effects of the Invention)

As described above, according to the present invention, the dielectric constant of 85 or higher and the resonant frequency temperature coefficient are flat and the quality coefficient of 6000 or higher at room temperature using a sintering aid stabilized by low production cost, low volatility, and reduced composition ratio of harmful components to human body. A ceramic dielectric having can be obtained. These dielectrics can be applied to microwave dielectrics because of their excellent dielectric constant and quality factor, and dielectrics having a resonance frequency of less than ± 5 ppm / ° C can also be widely used as EMI filter dielectrics and temperature compensation capacitors. In addition, by adding much cheaper samarium oxide (SmO) instead of expensive NdO, it is possible to reduce the manufacturing cost by lowering the weight ratio of the raw material itself. In addition, it is possible to reduce the problems with the volatilization of lead oxide and bismuth oxide can be used in the manufacturing process, it has an effect that can reduce the harmful elements to the human body.

Claims (3)

A dielectric composition comprising barium oxide, lead oxide, samarium oxide, and titanium dioxide as a main component, the dielectric ceramic composition having a composition formula as follows. x (BaO _1-a , PbO _a )-ySm ₂ O ₃ -zTiO ₂ 6 ≤ X ≤ 20 6 ≤ Y ≤ 20 Where 60 ≦ Z ≦ 75 0 ≤α≤0.2 (X + Y + Z = 100) The dielectric ceramic composition according to claim 1, wherein barium oxide (BaCO ₃ ) is used instead of barium oxide (BaO). The dielectric ceramic composition of claim 1, wherein lead trioxide (Pb ₃ O ₄ ) is used instead of lead oxide (PbO).