Dielectric ceramic composition for microwave use

Abstract

A dielectric ceramic composition for microwave use having a relative permittivity εr of 35 to 45, Qf0 value of more than 50,000 GHz (at 7 GHz), and dielectric characteristic of τf=0±10 ppm/° C includes an La2O3.Al2O3.SrO.TiO2 based ceramic composition and a specific quantity of Ga2O3 to increase the Qf0 value and a specific amount of Pr2O3to control the τf value.

Description

TECHNICAL FIELD

The present invention relates to a dielectric ceramic composition for microwave use having a relative permittivity εr of 35 to 45, Qf 0 value of at least 50,000 GHz (at 7 GHz) and a dielectric characteristic of τf=0±10 ppm/° C. employed for microwave communication filters, milliwave communication filters, oscillators, inductor antennas, and frequency adjusting rods etc.

BACKGROUND ART

Dielectric ceramic compositions are widely employed in the high-frequency region such as microwaves and milliwaves in for example dielectric resonators, dielectric substrates for MIC and waveguides. The characteristics that these are required to have are: (1) a large relative permittivity εr to meet demands for miniaturization, since the wavelength is reduced to 1/εr 1/2 in a dielectric, (2) low dielectric loss at high frequency i.e. high Q value, and (3) small and stable temperature coefficient τf of resonance frequency.

Conventional examples of such a dielectric ceramic composition are La—Ti—Al—O based compositions (see Japan, J. Appl. Phys. 36 (1997) 6814), which have εr=36, Qf 0 value=45,000 GHz, and τf=−2 ppm/° C., but their Qf 0 values are low.

Also, in the case of Ba(Zn 1/3 Nb 2/3 )O 3 based compositions (published in: Electronics/Ceramics September 1993 September page 3), εr=41, Qf 0 value=86,000 GHz, and τf=+31 ppm/° C., but a dielectric ceramic composition of small τf is not obtained.

Recently, La 2 O 3 .Al 2 O 3 .SrO.TiO 2 based composition or La 2 O 3 .Al 2 O 3 .SrO.TiO 2 .CaO based composition or composition containing one or two or more of Ce, Nb, Ta, Y, Zr, V, Cr, Mo, W, Co, Ni, Cu, Zn, Sn, Bi, B, or Si in the aforementioned ceramic compositions (see Laid-open Japanese Patent Publication H. 11-130528) has been proposed.

Regarding the dielectric characteristic of these ceramic compositions, they have excellent dielectric characteristics with εr of more than 30, Qf 0 value more than 25,000 GHz (at 1 GHz) and τf less than +30 (ppm/° C.), but dielectric ceramic compositions of low τf are not obtained. Recently, with increasingly severe demands for miniaturization of portable terminal electronic equipment, materials of even better dielectric performance are being demanded.

DISCLOSURE OF THE INVENTION

In view of the foregoing demands, an object of the present invention is to provide a dielectric ceramic composition for microwave use having a relative permittivity εr of 35 to 45, Qf 0 value of at least 50,000 GHz (at 7 GHz) and a dielectric characteristic of τf=0±10 ppm/° C.

The present invention studied various compositions with the object of obtaining a material capable of being controlled to a relative permittivity εr of 35 to 45, Qf 0 value of at least 50,000 GHz (at 7 GHz) and a dielectric characteristic of τf=0±10 ppm/° C, and, as a result, discovered that, with an La 2 O 3 .Al 2 O 3 .SrO.TiO 2 based ceramic composition, by adding a specific quantity of Ga 2 O 3 to the aforesaid ceramic composition, the Qf 0 value could be increased, and, by further adding a specific quantity of Pr 2 O 3 , control of the τf value became possible, so that a ceramic composition capable of being controlled to a relative permittivity εr of 35 to 45, Qf 0 value of at least 50,000 GHz (at 7 GHz) and a dielectric characteristic of τf=0±10 ppm/° C could be obtained, and thereby perfected the present invention.

Specifically, the present invention consists in a dielectric ceramic composition for microwave use characterized in that the compositional formula is expressed by aAl 2 O 3 .bGa 2 O 3 .cTiO 2 .dSrO.eLa 2 O 3 .fPr 2 O 3 , where a, b, c, d, e and f representing the mol ratios satisfy the following values (the case where b and f are simultaneously 0 is excluded).

a+b+c+d+e+f=1

0.079≦a≦0.167

0≦b≦0.017

0.333≦c≦0.412

0.333≦d≦0.412

0.035≦e≦0.167

0≦f≦0.101

BEST MODE FOR CARRYING OUT THE INVENTION

The reasons why, in the present invention, if the respective mol ratios of Al 2 O 3 , Ga 2 O 3 , TiO 2 , SrO, La 2 O 3 and Pr 2 O 3 are a, b, c, d, e, f, these mol ratios are respectively restricted to 0.079≦a≦0.167, 0≦b≦0.017, 0.333≦c≦0.412, 0.333≦d≦0.412, 0.035≦e≦0.167, and 0≦f≦0.101 are as follows.

If a is less than 0.079, εr increases but the Qf 0 value is less than 50,000 GHz, but if it exceeds 0.167 mol ratio, εr is lowered and drops to 35 or lower, which is undesirable.

If b exceeds 0.017 mol ratio, the Qf 0 value is lowered, resulting in the Qf 0 value dropping below 50,000 GHz, which is undesirable.

If c is less than 0.333 mol ratio, or is lowered, falling to 35 or lower, which is undesirable; if it exceeds 0.412 mol ratio, εr increases, but the Qf 0 value drops below 50,000 GHz, which is undesirable.

If d is less than 0.333 mol ratio, εr is lowered, falling to 35 or lower, which is undesirable; if it exceeds 0.412 mol ratio, εr increases, but the Qf 0 value drops below 50,000 GHz, which is undesirable.

If e is less than 0.035 mol ratio, εr is increased, but the Qf 0 value drops below 50,000 GHz, which is undesirable; if it exceeds 0.167 mol ratio, εr is lowered, falling to 35 or lower, which is undesirable.

If f exceeds 0.101 mol ratio, If becomes quite large, becoming 10 ppm/° C. or more, which is undesirable.

EXAMPLES

Example 1

As starting raw-material powders, high purity powder of Al 2 O 3 , Ga 2 O 3 , TiO 2 , SrCO 3 , La 2 O 3 and Pr 6 O 11 were blended as shown in Table 1, calcined for two hours at 1200° C., then pulverized to 1.0 μm then granulated by adding a binder and molded into discs of diameter 12 mm×thickness 25 mm with a molding pressure of 1.5 T/cm 2 . After this, the binder was removed and sintering was performed for four hours at 1500° C. in the atmosphere. The sintered body obtained was then cut to a diameter of 10 mm×thickness 4.5 mm to obtain samples. The samples of the Examples which were obtained were evaluated in regard to dielectric performance by the H&C method using a network analyzer. The results are shown in Table 2.

Comparative Example 1

For comparison, powder of high purity identical with that of Example 1 was blended as shown in Table 1, a molding manufactured, and samples manufactured by obtaining a sintered body. The samples of the Comparative Examples which were obtained were evaluated in regard to dielectric performance by the H&C method using a network analyzer. The results are shown in Table 2.

	TABLE 1
	Composition
	aAl 2 O 3 .bGa 2 O 3 .cTiO 2 .dSrO.eLa 2 O 3 .fPr 2 O 3
	a	b	c	d	e	f
present
invention
1	0.124	0.000	0.375	0.375	0.113	0.013
2	0.114	0.010	0.375	0.375	0.113	0.013
3	0.114	0.011	0.375	0.375	0.063	0.062
4	0.097	0.010	0.394	0.394	0.053	0.052
5	0.132	0.013	0.355	0.355	0.073	0.072
6	0.114	0.011	0.375	0.375	0.125	0.000
comparative
example
7	0.067	0.004	0.429	0.429	0.028	0.043
8	0.180	0.009	0.310	0.310	0.172	0.019
9	0.103	0.021	0.375	0.375	0.113	0.013
10	0.150	0.008	0.342	0.342	0.047	0.111
11	0.125	0.000	0.375	0.375	0.125	0.000

	TABLE 2
	Dielectric characteristic
			Temperature
	Relative		coefficient
	permittivity	Qf value	τf
	εr	(GHz)	(ppm/° C.)
present
invention
1	38.3	54000	−3.3
2	38.0	72000	−3.1
3	38.1	68000	+0.5
4	42.0	52000	+0.8
5	35.5	80000	+0.6
6	38.1	73000	−9.0
comparative
example
7	45.0	38000	+2.3
8	31.0	110000	−8.0
9	38.0	29000	−9.5
10	38.2	51000	+13.2
11	38.3	50000	−15.0

INDUSTRIAL APPLICABILITY

According to the present invention, in a La 2 O 3 .Al 2 O 3 .SrO.TiO 2 based ceramic composition, by adding specific amounts of Ga 2 O 3 and Pr 2 O 3 , a dielectric ceramic composition for microwave use having relative permittivity εr of 35 to 45 and Qf 0 value of more than 50,000 GHz (at 7 GHz), and dielectric characteristic of τf=0±10 ppm/° C. can be provided; this is a very suitable material for filters for microwave communication, filters for milliwave communication, oscillators, dielectric antennas, and frequency regulating rods etc.

Claims

1. A dielectric ceramic composition for microwave use wherein the compositional formula is expressed by aAl2O3.bGa2O3.cTiO2.dSrO.eLa2O3.fPr2O3 where a, b, C, d, e and f represent the mol ratios and satisfy the following values:a+b+c+d+e+f=1 0.079≦a≦0.167 0<b≦0.017 0.333≦c≦0.412 0.333≦d≦0.412 0.035≦e≦0.167 0≦f≦0.101.

2. A dielectric ceramic corn position according to claim 1, wherein 0.010≦b≦0.017.

3. A dielectric composition according to claim 1, wherein 0 <f≦0.101.

4. A dielectric composition according to claim 3, wherein 0.013≦f≦0.101.

5. A dielectric composition according to claim 4, wherein said composition has a relative permittivity, εr, of 35 to 45, a Qf0 value of at least 50,000 GHz at 7 Ghz, and a dielectric characteristic of τf=0±10 ppm/° C.