High-frequency dielectric ceramic composition, dielectric resonator, dielectric filter, dielectric duplexer, and communication apparatus

Abstract: A high-frequency dielectric ceramic composition comprises Ba, Ti, Nd, Sm, and Pr as primary components represented by the formula xBaO-yTiO 2 -z{(1-m-n)Nd 2 O 3 -mSm 2 O 3 -nPr 2 O 11/3 } wherein coefficients x, y, z, m, and n represent molar ratios, x + y + z = 1 , 0 < m ≤ 0.40, 0 < n ≤ 0.25, and the coefficients x, y, and z are in an area bounded by points A, B, C and D in a ternary diagram, wherein point A is at (x = 0.16, y = 0.70, z = 0.14), point B is at (x = 0.16, y = 0.68, z = 0.16), point C is at (x = 0.13, y = 0.68, z = 0.19), and point D is at (x = 0.13, y = 0.70, z = 0.17); wherein the composition further comprises a Bi compound in an amount of more than 0 parts by weight to 9 parts by weight on the basis of Bi 2 O 3 and an Fe compound in an amount of more than 0 parts by weight to 0.3 parts by weight on the basis of Fe 2 O 3 as additional components with respect to 100 parts by weight of the primary components. The high-frequency dielectric ceramic composition exhibits high reduction resistance during a sintering process, has a high relative dielectric constant ε r and a stable Q value in a microwave band, and can control the temperature coefficient τf of the resonant frequency to an appropriate value in the vicinity of zero ppm/°C.

Description: The present invention relates to a high-frequency dielectric ceramic composition, and to a dielectric resonator, a dielectric filter, a dielectric duplexer, and a communication apparatus using the same. Dielectric ceramic components are widely used as dielectric resonators and dielectric filters which are mounted in electronic devices, such as portable phones, personal radio equipment, and satellite broadcasting receivers, used in high-frequency bands including microwave bands and millimeter-wave bands. These high-frequency dielectric ceramic components require high dielectric constants and high Q values, and adjusting of the temperature coefficient of the resonant frequency to appropriate values near zero. Examples of disclosed dielectric ceramic compositions include a BaO-Nd 2 O 3 -TiO 2 -PbO composition (disclosed in Japanese Examined Patent Publication No. 56-26321), a BaO-Nd 2 O 3 -TiO 2 -Bi 2 O 3 composition (disclosed in Japanese Examined Patent Publication No. 59-51091), a BaO-Nd 2 O 3 -Ce 2 O 4 -Sm 2 O 3 -TiO 2 -Bi 2 O 3 -Fe 2 O 3 composition (disclosed in Japanese Laid-open No. 63-237304), and a BaO-Nd 2 O 3 -Sm 2 O 3 -TiO 2 -Bi 2 O 3 composition (disclosed in Japanese Laid-open No. 4-104946). These conventional BaO-Nd 2 O 3 -TiO 2 -PbO and BaO-Nd 2 O 3 -TiO 2 -Bi 2 O 3 compositions have low Q values with respect to relative dielectric constants ε r , which are of insufficient levels for dielectric resonators. In the BaO-Nd 2 O 3 -Ce 2 O 4 -Sm 2 O 3 -TiO 2 -Bi 2 O 3 -Fe 2 O 3 composition, the Q value is improved but the relative dielectric constant is decreased to an insufficient level in practical use by the addition of Fe 2 O 3 . Although the BaO-Nd 2 O 3 -Sm 2 O 3 -TiO 2 -Bi 2 O 3 composition has a high Q value, the Q value is unstable due to oxygen defects which are formed by reduction during a sintering process. Patent Abstracts of Japan, Volume 017, No. 630 (E-1463), November 22, 1993 corresponding to JP 05205520 discloses a dielectric porcelain composition expressed by x{(BaO) 1-w (SrO) w }.ySm 2 O 3 .zTiO 2 , wherein 0.10 ≤(x) ≤0.20, 0.10 < (y) ≤0.20, 0.60 ≤(z) ≤0.75 and 0.02 ≤(w) ≤0.30, respectively, and (x) + (y) + (z) = 1. Further, this document discloses x{(BaO) 1 - w (SrO) w }.y{(Sm 2 O 3 ) 1 - v (Ln 2 O 3 ) v }.zTiO 2 (wherein Ln represents at least either one of Nd and Pr), wherein 0.10 ≤(x) ≤0.20, 0.10 ≤(y) ≤0.20, 0.60 ≤(z) ≤0.75, 0.02 ≤(w) ≤0.30, and 0 <(v) ≤0.80, respectively, and (x) + (y) + (z) = 1. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a high-frequency dielectric ceramic composition which does not cause the formation of oxygen defects, that is, exhibits high reduction resistance during a sintering process, which has a high relative dielectric constant ε r and a stable Q value in a microwave band, and which can control the temperature coefficient τf of the resonant frequency to an appropriate value in the vicinity of zero ppm/°C. This object is achieved with a high frequency dielectric ceramic composition having the features of claim 1. It is another object of the present invention to provide a dielectric resonator, a dielectric filter, a dielectric duplexer, and a communication apparatus using this high-frequency dielectric ceramic composition. These objects are achieved with a dielectric resonator having the features of claim 2, a dielectric filter having the features of claim 3, a dielectric duplexer having the features of claim 4 and a communication apparatus having the features of claim 5, respectively. According to an aspect of the present invention, a high-frequency dielectric ceramic composition essentially consists of xBaO-yTiO 2 -z{(1-m-n)Nd 2 O 3 -mSm 2 O 3 -nPr 2 O 11/3 } wherein coefficients x, y, z, m, and n represent molar ratios, x + y + z = 1, 0 < m ≤ 0.40, 0 < n ≤ 0.25, and the coefficients x, y, and z are in an area bounded by points A, B, C and D in a ternary diagram, wherein point A is at (x = 0.16, y = 0.70, z = 0.14), point B is at (x = 0.16, y = 0.68, z = 0.16), point C is at (x = 0.13, y = 0.68, z = 0.19), and point D is at (x = 0.13, y = 0.70, z = 0.17); wherein the composition further comprises a Bi compound in an amount of more than 0 parts by weight to 9 parts by weight in terms of Bi 2 O 3 and an Fe compound in an amount of 0.01 or more parts by weight to 0.3 parts by weight in terms of Fe 2 O 3 as additional components with respect to 100 parts by weight of xBaO-yTiO 2 -z{(1-m-n)Nd 2 O 3 -mSm 2 O 3 -nPr 2 O 11/3 } According to another aspect of the present invention, a dielectric resonator comprises a dielectric ceramic component and input/output terminals, the dielectric resonator operating by electromagnetically coupling the dielectric ceramic component to the input/output terminals, wherein the dielectric ceramic component comprises the above high-frequency dielectric ceramic composition. According to another aspect of the present invention, a dielectric filter comprises the above dielectric resonator and external coupling means. According to another aspect of the present invention, a dielectric duplexer comprises at least two dielectric filters, input/output connecting means, each connected to each of the dielectric filters, and an antenna connecting means commonly connected to the dielectric filters, wherein at least one of the dielectric filters is the above dielectric filter. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a ternary diagram representing the ratio of primary components in a high-frequency dielectric ceramic composition in accordance with the present invention; Fig. 2 is an isometric view of a dielectric resonator of the present invention; Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2; Fig. 4 is an isometric view of a dielectric filter in accordance with the present invention; Fig. 5 is an isometric view of a dielectric duplexer in accordance with the present invention; and Fig. 6 is a block diagram of a communication apparatus in accordance with the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 2 is an isometric view of a dielectric resonator of the present invention, and Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2. With reference to Figs. 2 and 3, a dielectric resonator 1 is of a transverse electromagnetic (TEM) mode type and is composed of a prismatic dielectric ceramic component 2 having a through-hole which is filled with an internal conductor 3a. The sides of the dielectric resonator 1 are covered with an external conductor 3b. When the dielectric ceramic component 2 is electromagnetically coupled with input/output terminals, that is, external couplers, the dielectric ceramic component 2 functions as a dielectric resonator. The dielectric ceramic component 2 is composed of a high-frequency dielectric ceramic composition in accordance with the present invention. Any shapes other than the prismatic shape and any modes other than the TEM mode, such as a transverse magnetic (TM) mode and a transverse electric (TE) mode may be employed in the present invention. Fig. 4 is an isometric view of a dielectric filter in accordance with the present invention. A dielectric filter 4 includes the above dielectric resonator, which is composed of the above dielectric ceramic component 2 having the through-hole, the internal conductor 3a, and the external conductor 3b, and the external coupler 5. Although the dielectric filter 4 shown in Fig. 4 is a block type, the dielectric filter 4 may be a discrete type. Fig. 5 is an isometric view of a dielectric duplexer in accordance with the present invention. A dielectric duplexer 6 includes two dielectric filters, an input connector 7 connected to one of the dielectric filters, an output connector 8 connected to the other dielectric filter, and an antenna connector commonly connected to these two dielectric filters. Each dielectric filter is composed of the dielectric ceramic component 2 having the through-hole, the internal conductor 3a, and the external conductor 3b. Although the dielectric duplexer 6 shown in Fig. 5 is a block type, the dielectric duplexer 6 may be a discrete type. Fig. 6 is a block diagram of a communication apparatus in accordance with the present invention. A communication apparatus 10 includes a dielectric duplexer 12, a transmission circuit 14, a receiving circuit 16, and an antenna 18. The transmission circuit 14 is connected to an input connector 20 of the dielectric duplexer 12, and the receiving circuit 16 is connected to an output connector 22 of the dielectric duplexer 12. The antenna 18 is connected to an antenna connector 24 of the dielectric duplexer 12. The dielectric duplexer 12 includes two dielectric filters 26 and 28. Each of the dielectric filters 26 and 28 is composed of the above dielectric resonator 1 and external coupler 30. The dielectric filter 26 is connected between the input connector 20 and the antenna connector 24, and the dielectric filter 28 is connected between the antenna connector 24 and the output connector 22. The high-frequency dielectric ceramic composition of the present invention contains xBaO-yTiO 2 -z{(1-m-n)Nd 2 O 3 -mSm 2 O 3 -nPr 2 O 11/3 } wherein coefficients x, y, z, m, and n represent molar ratios, x + y + z = 1, 0 < m ≤ 0.40, 0 < n ≤ 0.25, and the coefficients x, y, and z are in an area bounded by points A, B, C and D in a ternary diagram shown in Fig. 1: point A (x = 0.16, y = 0.70, z = 0.14), point B (x = 0.16, y = 0.68, z = 0.16), point C (x = 0.13, y = 0.68, z = 0.19), and point D (x = 0.13, y = 0.70, z = 0.17); wherein the composition further comprises a Bi compound in an amount of more than 0 parts by weight to 9 parts by weight on the basis of Bi 2 O 3 and an Fe compound in an amount of 0.01 or more parts by weight to 0.3 parts by weight on the basis of Fe 2 O 3 as additional components with respect to 100 parts by weight of xBaO-yTiO 2 -z{(1-m-n)Nd 2 O 3 -mSm 2 O 3 -nPr 2 O 11/3 }. This composition barely forms oxygen defects in the ceramic composition during a sintering process, has high reduction resistance, has a high relative dielectric constant ε r and a high and stable Q value, and is capable of controlling the temperature coefficient τf of the resonant frequency to an appropriate level near zero ppm/°C. Examples The present invention will now be described with reference to the following Examples. Barium carbonate (BaCo 3 ), neodymium oxide (Nd 2 O 3 ), samarium oxide (Sm 2 O 3 ), praseodymium oxide (Pr 2 O 11/3 ), and titanium oxide (TiO 2 ) were prepared as starting materials for primary components, and bismuth oxide (Bi 2 O 3 ) and iron oxide (Fe 2 O 3 ) were prepared as starting materials for additional components (all the materials were powdered). In each sample, these materials were weighed in a ratio shown in Table 1, wherein coefficients x, y, z, m, and n represented molar ratios of the primary components in the formula xBaO-yTiO 2 -z{(1-m-n)Nd 2 O 3 -mSm 2 O 3 -nPr 2 O 11/3 }, and the Bi 2 O 3 content and the Fe 2 O 3 content were represented by parts by weight to 100 parts by weight of the primary components. These materials were wet-mixed using a ball mill, and the mixture was dehydrated, dried, and then calcined at 1,000 to 1,200°C for at least one hour. The calcined product was pulverized and was mixed with an organic binder. The mixture was molded and was sintered at 1,300 to 1,400°C in air or a nitrogen atmosphere containing less than 0.1 percent by volume of oxygen to prepare a disk sintered compact having a diameter of 10 mm and a thickness of 5 mm. The specific dielectric constant ε r and the Q value of the sintered compact were measured at 25°C and at a frequency of 4 to 5 GHz by a terminal-short-circuiting-type dielectric resonator method wherein the Q value was converted to a value at 1 GHz based on the rule Q×f = constant. The temperature coefficient τf of the resonance frequency between 25°C and 55°C was determined from TEM mode resonance frequencies. The results are shown in Table 1, wherein the sample marked with an asterisk indicates that the composition of the sample is outside of the range of the present invention. Sample No. Main Components (molar ratio) Additional Components (parts by weight) Sintered in Air Sintered in Nitrogen x y z m n Bi 2 O 3 Fe 2 O 3 ε r Q τ f ε r Q τ f *1 0.170 0.700 0.130 0.30 0.17 6.0 0.03 88 5800 35 91 5850 37 2 0.145 0.690 0.165 0.15 0.17 6.0 0.03 92 7280 7 92 7320 8 *3 0.130 0.665 0.205 0.30 0.17 6.0 0.03 Not sintered Not sintered *4 0.120 0.700 0.180 0.30 0.17 6.0 0.03 75 4130 -9 75 4150 -5 *5 0.160 0.665 5 0.175 0.30 0.17 6.0 0.03 Not sintered Not sintered *6 0.170 0.680 0.150 0.30 0.17 6.0 0.03 62 4320 45 61 4300 48 *7 0.145 0.690 0.165 0.60 0.17 6.0 0.03 88 7860 -20 87 7880 -19 *8 0.145 0.690 0.165 0.30 0.17 6.0 0 91 7320 2 90 1640 3 9 0.145 0.690 0.165 0.30 0.17 6.0 0.01 91 7420 1 90 5340 4 10 0.145 0.690 0.165 0.30 0.17 6.0 0.03 91 7500 3 90 7550 5 11 0.145 0.690 0.165 0.30 0.17 6.0 0.10 90 7520 0 90 7590 4 12 0.145 0.690 0.165 0.30 0.17 6.0 0.30 90 7640 0 89 7660 4 *13 0.145 0.690 0.165 0.30 0.17 6.0 3.00 77 3720 -19 77 1920 -24 *14 0.145 0.690 0.165 0.30 0.17 6.0 5.00 54 2520 -35 52 1920 -49 *15 0.145 0.690 0.165 0.30 0.17 0 0.03 85 9960 45 84 9990 57 *16 0.120 0.680 0.200 0.30 0.17 6.0 0.03 60 2270 31 61 2250 33 17 0.145 0.690 0.165 0.30 0.17 9.0 0.03 90 6280 4 82 6120 6 *18 0.145 0.690 0.165 0.30 0.17 12.0 0.03 73 4440 20 64 4470 31 *19 0.145 0.690 0.165 0 0 6.0 0.03 84 6200 15 85 6240 17 *20 0.145 0.690 0.165 0 0.17 6.0 0.03 92 6120 31 90 6150 29 *21 0.130 0.710 0.160 0.30 0.17 6.0 0.03 82 5260 28 84 5240 36 *22 0.160 0.710 0.130 0.30 0.17 6.0 0.03 91 6270 45 91 6220 48 *23 0.145 0.690 0.165 0.30 0 6.0 0.03 82 7620 -22 85 7610 -20 24 0.145 0.690 0.165 0.30 0.10 6.0 0.03 90 7580 0 89 7550 2 25 0.145 0.690 0.165 0.30 0.25 6.0 0.03 93 7480 5 92 7420 8 *26 0.145 0.690 0.165 0.30 0.50 6.0 0.03 96 6100 24 94 6120 27 27 0.160 0.700 0.140 0.30 0.17 6.0 0.03 89 7100 11 89 7120 13 28 0.160 0.680 0.160 0.30 0.17 6.0 0.03 84 6960 8 83 6870 10 29 0.130 0.680 0.190 0.30 0.17 6.0 0.03 82 6740 12 80 6670 15 30 0.130 0.700 0.170 0.30 0.17 6.0 0.03 85 7080 2 85 6920 4 Table 1 shows that the samples having the compositions in accordance with the present invention exhibit high specific dielectric constant ε r and high Q values. Moreover, the temperature coefficient τf ppm/°C of the resonance frequency can be controlled to an appropriate value near zero ppm/°C. Also, the samples of the present invention, which are sintered in a nitrogen atmosphere, have high Q values, since oxygen defects are not formed in the ceramic composition. In summary, at an Fe content of 0.3 percent or less and 0.01 percent or more by weight on the basis of Fe 2 O 3 , the reduction resistance can be improved without causing a decreased specific dielectric constant ε r . At a Pr 2 O 11/3 content n in a range of 0 < n ≤ 0.25, a sufficiently high specific dielectric constant ε r and a high Q value are achieved. Comparing sample 8 outside of the present invention and sample 10 in accordance with the present invention, the ceramic composition in accordance with the present invention, which contains a small amount of Fe 2 O 3 as an additional component, exhibits high reduction resistance without a decreased Q value after sintering in a nitrogen atmosphere. Comparing sample 10 in accordance with the present invention with sample 23 outside of the present invention, a sufficiently high specific dielectric constant ε r and a desirable temperature coefficient τf of the resonance frequency near zero are obtainable only when the Pr 2 O 11/3 content is in the above range. With reference to Fig. 1 and Table 1, the reasons for limitation of the contents of the primary components represented by the formula xBaO-yTiO 2 -z{(1-m-n)Nd 2 O 3 -mSm 2 O 3 -nPr 2 O 11/3 } and the additional Bi and Fe components will be described. The coefficient x representing the BaO content is in a range of 0.13 ≤ x ≤ 0.16 as shown in the ternary diagram in Fig. 1. When x < 0.13, both the specific dielectric constant ε r and the Q value are low (see Samples 4 and 16 in Table 1). When x > 0.16, the Q value is low and the temperature coefficient τf of the resonance frequency significantly shifts to a positive side (see Samples 1 and 6). The coefficient y representing the TiO 2 content is in a range of 0.68 ≤ y ≤ 0.70 as shown in the ternary diagram in Fig. 1. When y < 0.68, sintering is unsatisfactory (see Samples 3 and 5 in Table 1). When y > 0.70, the temperature coefficient τf of the resonance frequency significantly shifts to a positive side (see Samples 21 and 22). The coefficient z is in a range of 0.14 ≤ z ≤ 0.19 as shown in the ternary diagram in Fig. 1. When z < 0.14, the temperature coefficient τf of the resonance frequency significantly shifts to a positive side (see Samples 1 and 22 in Table 1). When z > 0.19, the specific dielectric constant ε r and the Q value are low, and the temperature coefficient τf of the resonance frequency significantly shifts to a positive side (see Samples 3 and 16). The coefficient m representing the Sm 2 O 3 content is in a range of 0 < m ≤ 0.40. When m = 0, the temperature coefficient τf of the resonance frequency significantly shifts to a positive side (see Sample 20 in Table 1). When m > 0.40, the temperature coefficient τf of the resonance frequency significantly shifts to a negative side (see Sample 7). The coefficient n representing the Pr 2 O 11/3 content is in a range of 0 < n ≤ 0.25. When n = 0, the specific dielectric constant ε r is low and the temperature coefficient τf of the resonance frequency significantly shifts to a negative side (see Sample 23 in Table 1). When n > 0.25, the Q value is low and the temperature coefficient τf of the resonance frequency significantly shifts to a positive side (see Sample 26). The Bi content on the basis of Bi 2 O 3 is more than 0 parts by weight to 9 parts by weight. When the Bi content is 0 parts by weight, the temperature coefficient τf of the resonance frequency significantly shifts to a positive side (see Sample 15). When the Bi content exceeds 9 parts by weight, the specific dielectric constant ε r and the Q value are low and the temperature coefficient τf of the resonance frequency significantly shifts to a positive side (see Sample 18). The Fe content on the basis of Fe 2 O 3 is 0.01 or more parts by weight to 0.3 parts by weight. When the Fe content is less than 0.01 parts by weight, the Q value decreases due to oxygen defects by reduction after sintering in a nitrogen atmosphere (see Sample 8). When the Fe content exceeds 0.30 parts by weight, the specific dielectric constant ε r and the Q value are low after sintering both in air and in a nitrogen atmosphere, and the temperature coefficient τf of the resonance frequency significantly shifts to a negative side (see Samples 13 and 14). In the above Examples, bismuth oxide Bi 2 O 3 and iron oxide Fe 2 O 3 are added as the additional components before calcination of the primary components. These additional components may be added to the primary components after calcination of the primary components. As described above, oxygen defects are barely formed in the ceramic composition during a sintering process in the present invention. Thus, the ceramic composition exhibits high reduction resistance during a sintering process, has a high relative dielectric constant ε r and a stable Q value in a microwave band, and can control the temperature coefficient τf of the resonant frequency to an appropriate value in the vicinity of zero ppm/°C. Thus, the dielectric resonator, the dielectric filter, the dielectric duplexer, and the communication apparatus using the dielectric ceramic component having the above composition have also satisfactory characteristics.

Claims: A high-frequency dielectric ceramic composition consisting essentially of xBaO-yTiO 2 -z{(1-m-n)Nd 2 O 3 -mSm 2 O 3 -nPr 2 O 11/3 } wherein coefficients x, y, z, m, and n represent molar ratios, x + y + z = 1, 0 < m ≤ 0.40,0 < n ≤ 0.25, and the coefficients x, y, and z are in an area bounded by points A, B, C and D in a ternary diagram, wherein point A is at (x = 0.16, y = 0.70, z = 0.14), point B is at (x = 0.16, y = 0.66, z = 0.16), point C is at (x = 0.13, y = 0.68, z = 0.19), and point D is at (x = 0.13, y = 0.70, z = 0.17); wherein the composition further comprises a Bi compound in an amount of more than 0 parts by weight to 9 parts by weight on the basis of Bi 2 O 3 and an Fe compound in an amount of 0.01 or more parts by weight to 0.3 parts by weight on the basis of Fe 2 O 3 as additional components with respect to 100 parts by weight of xBaO-yTiO 2 -z{(1-m-n)Nd 2 O 3 -mSm 2 O 3 -nPr 2 O 11/3 }. A dielectric resonator comprising a dielectric ceramic component and input/output terminals, the dielectric resonator operating by electromagnetically coupling the dielectric ceramic component to the input/output terminals, wherein the dielectric ceramic component comprises a high-frequency dielectric ceramic composition according to claim 1. A dielectric filter comprising a dielectric resonator according to claim 2 and external coupling means. A dielectric duplexer comprising: at least two dielectric filters; input/output connecting means, each connected to each of the dielectric filters; and antenna connecting means commonly connected to the dielectric filters; wherein at least one of the dielectric filters is a dielectric filter according to claim 3. A communication apparatus comprising: a dielectric duplexer according to claim 4; a transmitting circuit connected to at least one input/output connecting means of the dielectric duplexer; a receiving circuit connected to at least another input/output connecting means which is different from said at least one input/output connecting means; and an antenna connected to the antenna connecting means of the dielectric duplexer.

Inventors: TAMURA HIROSHI, WADA TAKAYA, TAMURA, HIROSHI, WADA, TAKAYA
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 2000
Main classification: C04B35
IPC codes: C04B35, H01P7, H01B3, H01P1