The use of dielectric ceramic compositions and dielectric microwave resonator

Abstract: A dielectric ceramic composition possessing a high relative dielectric constant, a high unloaded Q, and an excellent temperature characteristic is expressed as xPbO-yZrO₂-zCaO, in the relation of x+y+z=l , wherein x, y, z are in mol percentage ranges of 0.125 ≦ x ≦ 0.49, 0.4 ≦ y ≦ 0.6, 0.ll ≦ z ≦ 0.275. A part of ZrO₂ of the composition formula may be replaced by (BlB2)O₂ (where Bl is Mg, Ca, Zn, Co, Ni, Mn, Cu, Al, Ga, or Y, and B2 is Nb, Ta, or W), or Sn.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric ceramic used in a microwave region, and a dielectric resonator using this ceramic. 2. Description of the Prior Art Recently, with the development of communications using electromagnetic waves in the microwave region, such as mobile telephones, portable telephones and satellite broadcasting, it is required to downsize the equipment. For this purpose, it is necessary to reduce the size of the individual components composing the equipment. The dielectric is incorporated in such devices as a dielectric resonator in the filter element or oscillator. The size of the dielectric resonator is inversely proportional to the square root of the dielectric constant of the dielectric material itself when using the same resonance mode, and therefore manufacture of a small-sized dielectric resonator requires a material of high dielectric constant. Besides, other requirements of the dielectric include low loss in the microwave region or the high unloaded Q value, small changes of the resonant frequency with temperature, or small changes of the dielectric constant depending on temperature. Dielectric materials hitherto used in this field include, among others, Ba(Zn 1/3 Ta 2/3 )O 3 , BaO-TiO 2 compositions, and their derivatives having some of the elements replaced by other elements. In all these materials, the relative dielectric constant is about 30, and it is too low to downsize the resonator. As a material with a higher dielectric constant, BaO-TiO 2 -Sm 2 O 3 composition was disclosed in U.S. Patent 4,330,631 (May 18, 1982). This material has a relative dielectric constant of about 80, a high unloaded Q of about 3000 at 2 to 4 GHz, and a small temperature coefficient of the relative dielectric constant. In addition, BaO-PbO-TiO 2 -Nd 2 O 3 is known to have a relative dielectric constant of over 90, as reported in the Journal of American Ceramic Society, Vol. 67 (1984), pp.278-281. However, for further reduction of the resonator size, materials of much higher dielectric constant are needed, but materials possessing both high unloaded Q and small temperature coefficient are not yet known. On the other hand, the value of the temperature coefficient of the dielectric constant is generally negative when the dielectric constant is higher, but some materials have a positive value such as PbZrO 3 . It is hence attempted to reduce the temperature coefficient by combining materials having positive and negative temperature coefficient values. Materials having negative temperature coefficient include TiO 2 and SrTiO 3 , among others, and materials having positive temperature coefficient are represented, for example, by PbO-ZrO 2 -Tb 4 O 7 which is disclosed in U.S.Patent 4,849,384 (July 18, 1989), as the system having lanthanide oxide added to PbO-ZrO 2 . This material has the relative dielectric constant of over 100, and contributes greatly to downsizing of the resonator, but the temperature coefficient of the resonant frequency, τ f , is about -1,000 ppm/°C, which shows a large change by temperature. JP-61-185983 discloses the piezoelectric binary solid solution (Pb 1-x Ca x )TiO 3 -(Pb 1-x Ca x )ZrO 3 where x = 0.1-0.3. It is used in ultrasonic transmitting and receiving devices. SUMMARY OF THE INVENTION It is hence a first object of the invention to present a material having a relative dielectric constant larger than that of the hitherto known material BaO-TiO 2 -Sm 2 O 3 , a low loss in the microwave region, and a small temperature coefficient of the resonant frequency. It is a second object of the invention to present a dielectric resonator smaller in size than the dielectric resonator using any hitherto known material. To achieve these objects, the invention presents the use of a sinter of a dielectric ceramic a composition expressed as xPbO-yZrO 2 -zCaO, where x+y+z=1 , and x, y, z are in mol ranges of 0.125 ≤ x ≤ 0.49, 0.4 ≤ y ≤ 0.6, 0.11 ≤ z ≤ 0.275, respectively. This composition possesses a high specific dielectric constant of over 40 in the microwave region of 2 to 6 GHz, and also a small temperature coefficient not exceeding 300 ppm/°C, and a high unloaded Q value of over 300. Further details are seen in the claims. The invention is further intended to improve the dielectric characteristics in the microwave region by replacing a part of the ZrO 2 of the formula expressed by xPbO-yZrO 2 -zCaO by (B1B2)O 2 (where B1 is one of Mg, Ca, Zn, Co, Ni, Mn, Cu, Al, Ga, Y, and B2 is one of Nb, Ta, Sb, W), or SnO 2 . BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing a part of the ternary system indicating a desired composition range of xPbO-yZrO 2 -zCaO, in which sample numbers correspond to Table 1. Fig. 2 is a composition diagram showing a desired composition range of (Pb 1-u Ca u )Zr 1-v Sn v O 3 system, in which sample numbers correspond to Table 5. Fig. 3 is a diagram showing a longitudinal sectional view and a lateral sectional view of a coaxial resonator. DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Using PbO, CaCO 3 , ZrO 2 as starting materials, they were weighed as specified according to x, y, z of the formula xPbO-yZrO 2 -zCaO so as to achieve the composition shown in Table 1. These powder materials were put in a polyethylene ball mill containing stabilized zirconia balls, purified water was added to the mixture, which was mixed for 17 hours. After mixing, the slurry was dried, and put in an alumina crucible, and was calcined for 2 hours at 750 to 850°C. The calcined material was crushed by a pulverizer, ground in the same ball mill for 17 hours and dried. A material powder was obtained. To this powder, 5% aqueous solution of polyvinyl alcohol was added as binder by 6 wt.%, and mixed, and the mixture was passed through a 0.495 mm (32-mesh) sieve, granulated, pressed and formed into a column of 13 mm in diameter and about 5 mm in thickness at 100 MPa. This pellet was heated to 600°C for 2 hours to burn out the binder. The residue was put into a magnesia container and sintered for 2 hours at 1,100 to 1,400°C depending on the composition while preventing evaporation of PbO by spreading calcined powder of the same composition in the surroundings. The obtained sinter was measured by the dielectric resonator method, and the resonant frequency and unloaded Q were determined. Besides, from the dimensions of the sinter and the resonant frequency, the relative dielectric constant was calculated. The resonant frequency was 2 to 6 GHz. At -25 · C and 85°C, the resonant frequency was measured, and the temperature coefficient (τ f ) was calculated on the basis of the value at 20°C. The results are shown in Table 1. As is clear from Table 1, in the composition in which x, y, z are respectively in the ranges of 0.125 ≤ x ≤ 0.49, 0.4 ≤ y ≤ 0.6, 0.11 ≤ z ≤ 0.275, the dielectric constant is as high as 40 to 165, and the unloaded Q is over 200, and the temperature coefficient of the resonant frequency does not exceed 150 ppm/°C. In particular, the sample numbers 5, 7, 11, 12 in which x, y, z are in the ranges of 0.28 ≤ x ≤ 0,425, 0.45 ≤ y ≤ 0.52, 0.125 ≤ z ≤ 0.2 present excellent characteristics with the relative dielectric constant of over 100, unloaded Q of over 300, and temperature coefficient of resonant frequency of 40 ppm/°C or less. However, the compositions not included in the above range, that is, the dotted range in Fig. 1 are not suitable as dielectrics for microwave devices. More specifically, in the compositions of which CaO is less than 0.11 (sample numbers 1, 2, 3, 10, 17 in Table 1), the unloaded Q is less than 200, or the temperature coefficient of the resonant frequency is over 200 ppm/°C, or both, and they are not applicable as dielectric resonators. In the composition of which CaO is more than 0.275 (sample number 9 in Table 1), the relative dielectric constant is less than 40. If ZrO 2 is less than 0.4 (sample 16 in Table 1), the unloaded Q is less than 200, and in the composition exceeding 0.6 (sample number 21 in Table 1), the dielectric is not sintered densely at temperature of less than 1,400°C. Embodiment 2 In addition to the starting materials of Embodiment 1, powders of MgO, ZnO, CoO, NiO, MnO 2 , CuO, Al 2 O 3 , Ga 2 O 3 , Y 2 O 3 , Nb 2 O 5 , Ta 2 O 5 , Sb 2 O 3 , WO 3 were weighed as specified so as to compose as shown in Table 2, according to u, v, m, and n of the composition formula, Pb 1-u Ca u Zr 1-v (B1 m B2 n ) v O 3 (where B1 is an element selected from a group of Mg, Ca, Zn, Co, Ni, Mn, Cu, Al, Ga, and Y, B2 is an element selected from a group of Nb, Ta, Sb, and W, and m and n are the values selected to satisfy the relation of am + bn = 4 , while keeping the relation of m+n=1 , supposing the valence of element B1 as a, and the valence of element B2 as b), and ceramics were prepared in the same manner as in Embodiment 1, and the dielectric characteristics were measured. The results are shown in Table 2. As clear from Table 2, in the compositions in which u and v of the formula (Pb 1-u Ca u )Zr 1-v (B1 m B2 n ) v O 3 are in the ranges of 0.25 ≤ u ≤ 0.5, and 0 < v ≤ 0.2, respectively, the dielectric constant is 60 or higher, the unloaded Q is 300 or higher, and the absolute value of temperature coefficient of resonant frequency is 100 ppm/°C or less. Besides, in the compositions of sample numbers 1 to 5 in which Zr is not replaced by (B1 m B2 n ) the results of two sintering processes did not match, but in the compositions having Zr replaced by (B1 m B2 n ) (sample numbers 18, 33, 36, 38, 40, 41, 42, 47), the sintering temperature is 1,250°C or less, and the results of the sintering test performed twice matched well. This is considered due to decrease of the sintering temperature, small evaporation of PbO, and hence the characteristics are stabilized. Embodiment 3 In addition to the starting materials in Embodiment 1, SnO 2 powder was used, and weighed as specified so that u and v in the formula (Pb 1-u Ca u )Zr 1-v Sn v O 3 may form the composition as shown in Table 3, and ceramics were prepared in the same manner as in Embodiment 1. The results of measuring the dielectric characteristics of these ceramics are shown in Table 3. As clear from Table 3, in the compositions in which u and v are in a range of a quadrangle having the following points as the vertices on the uv plane shown in Fig. 2; A (u=0.3 v=0.0), B (u=0.5 v=0.0), C (u=0.4 v=0.6), D (u=0.25 v=0.6), the dielectric constant is 60 or higher, the unloaded Q is 700 or higher, and the absolute value of the temperature coefficient of resonant frequency is 100 ppm/°C or less. As compared with the compositions not containing Sn shown in sample numbers 1 to 4, although the unloaded Q is improved, in the compositions not within the quadrangle ABCD, any one of the following arises, the dielectric constant is 60 or less, the unloaded Q is 700 or less, or the temperature coefficient of the resonant frequency is 100 ppm/°C or more, and the desired characteristics as the dielectric for the microwave region are not obtained. Embodiment 4 Of the compositions disclosed in Embodiments 1, 2 and 3, those shown in Table 4 are selected, and coaxial dielectric resonators shown in Fig. 3 were fabricated. The fabricating method of the dielectric resonators is described below. The powder combined with binder as shown in Embodiment 1 was pressed and formed into a cylindrical sample of 8.3 mm in outer diameter, 2.5 mm in inner diameter, and about 10 mm in height, and after burning out the binder, the material was sintered in the sintering method in Embodiment 1, and a cylindrical sinter 10 was fabricated. The sintered sample was coated with a silver paste on the inner wall, outer wall and one bottom of the cylindrical sinter 10 as shown in Fig. 3, and it was dried and baked at 800 · C for 15 minutes, and an electrode 20 was manufactured. The inner diameter 2a, outer diameter 2b, height (length) L, resonant frequency, Q, and temperature coefficient τ f of the resonant frequenty of the thus manufactured coaxial dielectric resonators are shown in Table 4. As shown in Table 4, the resonators using the dielectrics of the invention are smaller in size than the resonators using the materials of the highest relative dielectric constant (90) among the hitherto known dielectrics, and at the same time it is evident that the Q value and temperature characteristics are equally comparable. Thus, the ceramic compositions used by the invention contain materials having a high relative dielectric constant of over 100 in the microwave region, and these materials also have a high unloaded Q value of 1,000 or more, and have a sufficiently small temperature coefficient practically. Therefore, the ceramic compositions used by the invention are not only useful as the material for dielectric resonator, but also effective for downsizing the circuit if applied in substrates for forming microwave circuits. Sample No. Composition firing temperature °C Relative dielectric constant Unloaded Q Temperature coefficient of resonant freq. τ f ppm/°C x PbO y ZrO 2 z CaO 1 0.5 0.5 0 1200 125 470 -1500 2 0.45 0.5 0.05 1250 134 95 -1250 3* 0.4 0.5 0.1 1300 195 70 -700 4 0.39 0.5 0.11 1300 165 280 +50 5 0.375 0.5 0.125 1300 162 310 -25 6 0.35 0.5 0.15 1350 142 560 +65 7 0.325 0.5 0.175 1350 115 820 +28 8 0.25 0.5 0.25 1350 52 810 -40 9 0.2 0.5 0.3 1400 35 750 -43 10 0.45 0.45 0.1 1150 180 80 -260 11 0.4 0.45 0.15 1150 124 410 -35 12 0.35 0.45 0.2 1150 106 300 -38 13 0.425 0.4 0.175 1100 85 450 -100 14 0.49 0.4 0.11 1100 120 200 -130 15 0.325 0.4 0.275 1200 66 430 -40 16 0.45 0.35 0.2 1100 72 130 -42 17 0.35 0.55 0.1 1350 180 45 -2000 18 0.3 0.55 0.15 1350 130 510 +80 19 0.29 0.6 0.11 1350 82 300 +50 20 0.125 0.6 0.275 1400 43 760 -40 21 0.2 0.65 0.15 not sinter - - - Sample No. Composition Firing temperature °C Relative dielectric constant Unloaded Q Temperature coefficient of resonant freq. τ f ppm/°C u Ca v Sn 1 0.3 0 1300 154 300 +90 2 0.35 0 1350 115 820 +60 3 0.4 0 1350 91 860 -24 4 0.5 0 1400 51 810 -59 5 0.3 0.05 1400 146 700 +95 6 0.35 0.05 1400 112 1190 +37 7 0.4 0.05 1400 94 1390 -15 8 0.25 0.1 1350 145 570 +120 9 0.3 0.1 1400 126 930 +89 10 0.35 0.1 1400 107 1330 +29 11 0.4 0.1 1400 91 1400 -29 12 0.35 0.15 1400 101 1340 +17 13 0.4 0.15 1400 88 1340 +2 14 0.35 0.2 1400 100 1310 +25 15 0.5 0.2 1450 46 1160 +103 16 0.35 0.3 1400 94 1270 +18 17 0.35 0.5 1400 87 1350 +9 18 0.25 0.6 1350 81 880 +11 19 0.4 0.6 1400 64 1400 -54 20 0.4 0.65 1400 53 1250 +86 sample No. Dielectric composition inner diameter (2a) mm outer diameter (2b) mm length (L) mm resonant frequency GHz Q τ f ppm/°C 1 Ba. 5 Pb. 5 Nd 2 Ti 6 O 14 7.11 2.14 8.98 878 420 +55 2 Pb .65 Ca .36 ZrO 3 6.85 2.06 7.76 881 430 +33 3 Pb .64 Ca .36 ZrO 3 6.99 2.11 8.15 890 430 +26 4 Pb .63 Ca .37 ZrO 3 7.00 2.11 8.20 897 450 +17 5 Pb .65 Ca .35 Zr .95 Sn .96 O 3 7.03 2.12 8.12 882 480 +28 6 Pb .65 Ca .36 Zr .926 Sn .976 O 3 7.05 2.12 8.20 884 470 +24 7 Pb .64 Ca .36 Zr .95 Sn .96 O 3 7.04 2.12 8.24 879 440 +20 8 Pb .62 Ca .38 Zr .92 (Ni 1/3 Nb 2/3 ) .68 O 3 6.82 2.05 8.38 870 400 +21

Claims: Use of a sinter of a dielectric ceramic composition in a dielectric microwave resonator, said composition having the formula xPbO-yZrO 2 -zCaO wherein x, y and z expressed in moles are 0.125 ≤ x ≤ 0.49 0.4 ≤ y ≤ 0.6 0.11 ≤ z ≤ 0.275 where x + y + z = 1 , with the proviso that (a) a part of the ZrO 2 may be replaced by (B1 m B2 n )O 2 and wherein y = 0.5, said dielectric ceramic composition having the formula Pb 1-u Ca u Zr 1-v (B1 m B2 n ) v O 3 , wherein B1 is an element selected from Mg, Ca, Zn, Co, Ni, Mn, Cu, Al, Ga and Y; B2 is an element selected from Nb, Ta, Sb and W; and u and v are 0.25 ≤ u ≤ 0.5 0 ≤ v ≤ 0.2 wherein m + n = 1 and a·m + b·n = 4 , wherein a is the valence of element B1 and b is the valence of element B2, or (b) a part of the ZrO 2 may be replaced by SnO 2 and wherein y= 0.5, said dielectric ceramic composition having the formula (Pb 1-u Ca u )Zr 1-v Sn v O 3 , wherein u and v are within a range of a quadrangle having vertexes at the following points A, B, C and D on the uv plane: A; u=0.3 v=0.0 B; u=0.5 v=0.0 C; u=0.4 v=0.6 D; u=0.25 v=0.6. The use of claim 1, wherein x, y and z in the formula xPbO-yZrO 2 -zCaO expressed in moles are 0.28 ≤ x ≤ 0.425 0.45 ≤ y ≤ 0.52 0.125 ≤ z ≤ 0.2 where x + y + z = 1 .

Inventors: KAGATA HIROSHI, KATO JUNICHI, KAGATA, HIROSHI, KATO, JUNICHI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1991
Main classification: C04B35
IPC codes: H01G4, C04B35, H01B3