KR970008711B1 - Microwave dielectric ceramics - Google Patents

Abstract

The ceramic composition comprises barium oxide, cerium oxide, lantan oxide and titanium dioxide having the following equations; x(Ba1-alpha= Pbalpha)O-y(ND2O3(1-beta.r)= CeO2(beta)= The ceramic composition comprises barim oxide, lead oxide, niodium La2O3r)-zTiO2(where, 6 < x 20, 10 < y < 20, 60< z < 75, 0 < alpha < 0.5, 0 < beta < 0.2, 0 < r < 0.2, 0 < 1-beta-r < 1, x+y+z= 100). In the electric ceramic composition, barium carbonate can use instead of the barium oxide, lead trioxide can also use instead of lead oxide.

Description

[Name of invention]

Dielectric Ceramic Composition for Microwave

Detailed description of the invention

[Field of Invention]

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

[Prior art]

Recently, as wireless communication means such as automobile telephone, cellular phone, cordless telephone and satellite broadcasting receiver have become widely used, the microwave band filter, substrate and voltage control oscillator (Voltage Controlled Oscillator: VCO) have been developed due to the development of microwave circuit and integrated circuit. ) Dielectric ceramics are widely used.

The microwave dielectric ceramic is mainly used as a resonator, and the ceramic composition used herein includes BaO-Nd ₂ O ₃ -TiO ₂ , BaO-Sm ₂ O ₃ -TiO ₂ , Pbo-ZrO ₂ -CaO Various dielectrics are used. BaO-Nd ₂ O ₃ -TiO ₂ and BaO-Sm ₂ O ₃ -TiO ₂ -based ceramics have a dielectric constant of about 60-80 and a quality factor of about 5000 at 1 GHz, but have a very high temperature coefficient of resonant frequency (τ _f ). There is a big problem in practical use.

In addition, the PbO-ZrO ₂ -CaO system proposed in Japan has a high dielectric constant of more than 90, but the quality factor at high frequencies is as low as 1000 to 3500, and the loss at high frequencies of 3GHz or more is high band pass filter (BPF) and voltage There is a disadvantage in that the loss of parts, such as adjustable oscillator.

As a required characteristic to be applied to such high-frequency components, the quality factor should be high (for example, 500 or more at 1 GHz), and the composition of the high frequency components may be changed in positive or negative direction with the temperature coefficient of resonant frequency centered at 0 ppm / ℃. It should be freely adjustable.

In addition, in order to reduce the size (λ / ε) of the resonator, a ceramic material having a large dielectric constant is required.

As a ceramic composition prepared for the purpose of improving such properties, BaO-Bi ₂ O ₃ -Nd ₂ O ₃ -TiO ₂ reported an improvement in permittivity due to the addition of bismuth oxide (BiO ₂ O ₃ ) and lead oxide (PbO). And BaO-PbO-Nd ₂ O ₃ -TiO ₂ -based compositions have been proposed (see Japanese Patent Laid-Open Nos. 62-78154 and 63-112458).

The dielectric constant of this composition is reported to be 80 or more and the quality factor is about 4000-5500.

However, since these compositions add excessive amounts of lead oxide and bismuth oxide in the manufacturing process, it is difficult to control uniform composition due to volatilization of these additive elements, and these additives are known as very harmful elements to the human body in the manufacturing process, and expensive oxidation Nidium is an essential dielectric composition.

[Problem to solve in the present invention]

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 resonant frequency should be as low as ± 5 ppm / ° C.

In addition to satisfying these dielectric properties, the conditions required in the manufacturing process prevent the disadvantages of difficult control of the composition due to volatilization of the component elements, thereby preventing quality deterioration, and lead (Pb) and bismuth components, which are harmful elements to the human body in the manufacturing process. It is to stably control the manufacturing composition by reducing the amount of elements.

[Purpose of invention]

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

[Configuration of Invention]

The present invention is a dielectric ceramic composition containing barium oxide, lead oxide, niobium oxide, cerium oxide, lanthanum oxide, and titanium dioxide as a main component. As a result of various experiments, new compositions are obtained as follows. For example, the present invention provides 6 to 20 mol% of (Ba ₁ -α · Pbα) 0 as the first component and 10 to 20 mol% of (Nd ₂ O _{3 (1-β-γ)} CeO _{2 as the second component. (β)} La ₂ O _{3 (Υ)} ), and the third component is composed of 60 to 70 mol% of TiO ₂ .

The present invention partially replaces cerium oxide and lanthanum oxide, which are less expensive than sodium oxide, in place of nitric oxide to increase the dielectric constant and quality coefficient, and obtain a composition in which the temperature coefficient of resonance frequency is close to 0 ppm / ° C. .

The dielectric ceramic of the present invention prepared by sintering the composition at a sintering temperature in the range of 1250 ° C. to 1400 ° C. for 2 hours to 4 hours has a dielectric constant of 90 or more and a resonance frequency temperature coefficient within ± 10 ppm / ° C., which is 1 GHz. It has a quality factor of more than 5000 at the resonance frequency.

EXAMPLE

Hereinafter, preferred embodiments of the present invention will be described in more detail.

In the present invention, various experiments were carried out using a small amount of cerium oxide and lanthanum oxide as additives while varying the composition of barium oxide, lead oxide, niobium oxide and titanium dioxide.

That is, x (Ba _1- αPb _α ) Oy (Nd ₂ O _{3 (1-β-γ)} CeO _{2 (β)} La ₂ O _{3 (γ)} )-zTiO ₂ composition was oxidized as shown in Table 1. Experiments were performed by dividing the composition of cerium, the composition of adding lanthanum oxide as shown in Table 2, and the composition of adding cerium oxide and lanthanum oxide together as shown in Table 3.

Mix the basal sample with deionized water, as listed in each table.

In this case, barium carbonate (BaCO ₃ ) may be used instead of barium oxide (BaO), and lead trioxide (Pb ₃ O ₄ ) may be used instead of lead oxide (PbO).

Mixing uses a ball milling method, zirconia balls and plastic jars.

The dried powder is calcined at 100 ° C. or higher for 2 hours, and an appropriate amount of polyvinyl alcohol is added and mixed in the zirconia trigger.

The mixed material is molded into cylindrical specimens of at least 10 mm in diameter and 5 mm in height using a mold and hydraulic press.

The pressure at the time of shaping | molding is 1.0 ton / cm <2> or more.

The molded specimen is sintered using an electric furnace at a high temperature above zirconia setter and in an air atmosphere at a temperature of 1250 ° C. or above, sintering conditions listed in each table.

The sintered specimens were measured for dielectric constant at about 3 GHz by the Hockey-Coleman method, and the no-load Q of the dielectric was measured by an open resonant method.

In addition, the temperature coefficient of the resonance frequency was calculated for the temperature range of 25 ° C to 125 ° C based on the resonance frequency with respect to the temperature of 25 ° C by the following equation (1).

… (One)

Resonant frequency at f (125) = 125 ° C

Resonant frequency at f (25) = 25 ° C

ΔT = measurement 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, as summarized in each table, the optimum sintering temperature decreases as the amount of titanium dioxide (TiO ₂ ) added (z) increases and the quality factor An increasing effect can be obtained.

However, when titanium dioxide is 75 mol% or more, the temperature coefficient of the resonance frequency is largely shifted in the positive direction, making it difficult to use practically.

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 niobium oxide (Nd ₂ O ₃ ) increases during the composition, the quality coefficient can be increased.However, the optimum sintering temperature is higher than 1400 ℃ and when the molar temperature is 20 mol% or more, the temperature coefficient of the resonance frequency moves in both directions. There are also disadvantages.

In addition, when the addition amount is 10 mol% or less, since the addition amount of titanium dioxide is relatively increased, the temperature coefficient of the resonance frequency is shifted in both directions.

Therefore, the preferable composition ratio of the niobium oxide component is about 10-20 mol%.

As the amount of lead oxide (PbO) added in the composition increases, the appropriate sintering temperature is lowered and the dielectric constant is increased.However, when 50 mol% or more is added, the dielectric constant increases but it is difficult to control the composition due to volatilization of lead oxide and the quality factor There is a disadvantage that is lowered.

In addition, if the amount of barium oxide in the composition is increased, the quality factor is lowered, but temperature stability of the resonance frequency can be obtained.

As the amount of cerium oxide (CeO ₂ ) and lanthanum oxide (La ₂ O ₃ ) increases, the dielectric constant and quality coefficient increase, and the appropriate sintering temperature decreases, but the temperature coefficient of the resonance frequency moves in both directions. .

Even if barium carbonate (BaCO ₃ ) is used instead of barium oxide (BaO) in the composition, there is no significant change in dielectric properties, and uniform mixing is achieved by using lead trioxide (Pb ₃ O ₄ ) instead of lead oxide (PbO). It does not have much influence on the dielectric properties.

In the same composition, the higher the sintering temperature, the higher the dielectric constant and the quality factor. The longer the sintering time, the higher the dielectric constant is, but the quality factor is slightly increased.

Dielectric properties of each sample prepared under different composition ratios and sintering conditions are summarized in Table 1, Table 2 and Table 3.

TABLE 1

Composition and manufacturing conditions and dielectric properties according to the addition of cerium oxide

(x + y + z = 100)

[Table 2]

Composition and manufacturing conditions and dielectric properties according to the addition of lanthanum oxide

(x + y + z = 100)

TABLE 3

Composition and manufacturing conditions and dielectric properties according to the addition of cerium oxide and lanthanum oxide

(x + y + z = 100)

[Effects of the Invention]

As described above, according to the present invention, the temperature coefficient of the dielectric constant and resonance frequency of 90 or more is flat at room temperature by using a sintering aid stabilized with low manufacturing cost, low volatility, and reduced composition ratio of harmful components to the human body. It is possible to obtain a dielectric having a quality factor of 5000 or more.

Since these dielectrics have excellent dielectric constant and quality factor, microwave dielectrics can be used, and dielectrics having a resonance temperature of within ± 10 ppm / ° C can also be widely used as EMI filter dielectrics and temperature compensation capacitors.

In addition, by adding much cheaper cerium oxide and lanthanum oxide instead of expensive sodium oxide (Nd ₂ O ₃ ), it is possible to reduce the manufacturing cost by lowering the weight ratio of the raw material itself.

Furthermore, since no bismuth oxide is added, the problem of volatilization of these components can be solved, and thus a general manufacturing process can be used, and the use of an element harmful to the human body can be reduced.

Claims (4)

A dielectric composition composed mainly of barium oxide, lead oxide, niobium oxide, cerium oxide, lanthanum oxide, and titanium dioxide, the dielectric ceramic composition having a composition formula as follows. x (Ba _1- αPb _α ) Oy (Nd ₂ O _{3 (1-β-γ)} CeO _{2 (β)} La | ₂ O _{3 (γ)} ) -zTiO ₂ The dielectric ceramic composition of claim 1, wherein barium carbonate (BaCO ₃ ) is used instead of barium oxide (BaO). The dielectric ceramic composition according to claim 1, wherein lead trioxide (Pb ₃ O ₄ ) is used instead of lead oxide (PbO). The dielectric ceramic composition of claim 1, wherein the composition is sintered at a sintering temperature of 1250 ° C. to 1400 ° C. and a sintering time of 2 hours to 4 hours.