Ferrite composition and electronic component

Abstract

A ferrite composition comprises a main component and a sub component. The main component is comprised of 40.0 to 49.8 mol % iron oxide in terms of Fe.sub.2O.sub.3, 5.0 to 14.0 mol % copper oxide in terms of CuO, 0 to 32.0 mol % zinc oxide in terms of ZnO, and a remaining part of nickel oxide. The sub component includes 0.5 to 4.0 wt % tin oxide in terms of SnO.sub.2, 0.10 to 1.00 wt % bismuth oxide in terms of Bi.sub.2O.sub.3, and 0.21 to 3.00 wt % cobalt oxide in terms of Co.sub.3O.sub.4, with respect to the main component.

Claims

1. A ferrite composition comprising a main component and a sub component, wherein said main component is comprised of 40.0 to 49.8 mol % iron oxide in terms of Fe.sub.2O.sub.3, 5.0 to 14.0 mol % copper oxide in terms of CuO, 0.5 to 26.0mol % zinc oxide in terms of ZnO, and a remaining part of nickel oxide, said sub component includes 0.5 to 4.0 wt % tin oxide in terms of SnO.sub.2, 0.10 to 1.00 wt % bismuth oxide in terms of Bi.sub.2O.sub.3, and 0.21 to 3.00 wt % cobalt oxide in terms of Co.sub.3O.sub.4, with respect to the main component 100 wt %, said ferrite composition has ferrite particles and crystal grain boundaries present among adjacent crystal particles, and an average crystal particle diameter of the crystal particles is 0.2 to 1.5 m.

2. An electronic component comprising a ferrite sintered body composed of the ferrite composition according to claim 1.

3. The ferrite composition according to claim 1, wherein the amount of iron oxide in terms of Fe.sub.2O.sub.3 is 42.0 to 49.0 mol %.

4. The ferrite composition according to claim 1, wherein the amount of iron oxide in terms of Fe.sub.2O.sub.3 is 43.0 to 49.0 mol %.

5. The ferrite composition according to claim 1, wherein the amount of tin oxide, in terms of SnO.sub.2, is 0.5 to 2.5 wt %.

6. The ferrite composition according to claim 1, wherein the amount of bismuth oxide, in terms of Bi.sub.2O.sub.3, is 0.20 to 0.70 wt %.

7. The ferrite composition according to claim 1, wherein the amount of bismuth oxide, in terms of Bi.sub.2O.sub.3, is 0.20 to 0.50 wt %.

8. The ferrite composition according to claim 1, wherein the amount of cobalt oxide, in terms of Co.sub.3O.sub.4, is 0.23 to 2.00 wt %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional view of a multilayer inductor according to one embodiment of the present invention.

(2) FIG. 2 is a cross-sectional view of a LC composite electronic component according to one embodiment of the present invention.

(3) FIG. 3 is a graph showing a relation between and Q of each sample in an external magnetic field H=100 A/m.

(4) FIG. 4 is a graph showing a relation between and Q of each sample in an external magnetic field H=200 A/m.

(5) FIG. 5 is a graph showing variations of Q of each sample when an external magnetic field H varies.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) Hereinafter, the present invention will be described based on embodiments shown in the drawings.

(7) As shown in FIG. 1, a multilayer inductor 1 according to one embodiment of the present invention has an element 2 and terminal electrodes 3. The element 2 is obtained by firing a green multilayer body in which coil conductors 5 are formed three-dimensionally and spirally via ferrite layers 4. The ferrite layers 4 are composed of a ferrite composition according to one embodiment of the present invention. The multilayer inductor 1 is obtained by forming the terminal electrodes 3 at both sides of the element 2 to connect the terminal electrodes 3 with leading electrodes 5a and 5b. A shape of the element 2 is not particularly limited, but it is usually rectangular parallelepiped one. Also, the size thereof is not particularly limited, either. A proper size can be adopted based on usage.

(8) Materials of the coil conductors 5 and the leading electrodes 5a and 5b are not particularly limited, and Ag, Cu, Au, Al, Pd, or Pd/Ag alloy etc. is used. Note that, Ti compound, Zr compound, or Si compound etc. may be added.

(9) The ferrite composition according to the present embodiment is NiCu ferrite or NiCuZn ferrite. The main component thereof may include iron oxide, copper oxide, and nickel oxide, or may further include zinc oxide.

(10) In the main component 100 mol %, in terms of Fe.sub.2O.sub.3, a content of iron oxide is 40.0 to 49.8 mol %, preferably 42.0 to 49.0 mol %, and more preferably 43.0 to 49.0 mol %. When the content of iron oxide is too small, Q value tends to decrease. When the content of iron oxide is too large, sinterability deteriorates and, in particular, sintered density after low temperature sintering tends to decrease.

(11) In the main component 100 mol %, in terms of CuO, a content of copper oxide is 5.0 to 14.0 mol %. When the content of copper oxide is too small, sinterability deteriorates and, in particular, sintered density after low temperature sintering tends to decrease. When the content of copper oxide is too large, Q value tends to decrease.

(12) In the main component 100 mol %, in terms of ZnO, a content of zinc oxide is 0 to 32.0 mol %. That is, zinc oxide may not be included as the main component. When zinc oxide is included as the main component, the content of zinc oxide is preferably 0.5 to 30.0 mol % and more preferably 0.5 to 26.0 mol %. When the content of zinc oxide is too large, Curie temperature tends to decrease.

(13) A remaining part of the main component is comprised of nickel oxide.

(14) In addition to the above main component, the ferrite composition according to the present embodiment includes tin oxide, bismuth oxide, and cobalt oxide as the sub component.

(15) With respect to the main component 100 wt %, in terms of SnO.sub.2, a content of tin oxide is 0.5 to 4.0 wt % and preferably 0.5 to 2.5 wt %. When the content of tin oxide is too small, Q value tends to decrease. When the content of tin oxide is too large, sinterability deteriorates and, in particular, sintered density after low temperature sintering tends to decrease.

(16) With respect to the main component 100 wt %, in terms of Bi.sub.2O.sub.3, a content of bismuth oxide is 0.10 to 1.00 wt %, preferably 0.20 to 0.70 wt %, and more preferably 0.20 to 0.50 wt %. When the content of bismuth oxide is too small, sinterability deteriorates and, in particular, sintered density after low temperature sintering tends to decrease. When the content of bismuth oxide is too large, Q value tends to decrease.

(17) With respect to the main component 100 wt %, in terms of Co.sub.3O.sub.4, a content of cobalt oxide is 0.21 to 3.00 wt % and preferably 0.23 to 2.00 wt %. When the content of cobalt oxide is too small, Q value tends to decrease. When the content of cobalt oxide is too large, sinterability deteriorates and, in particular, sintered density after low temperature sintering tends to decrease.

(18) In the ferrite composition according to the present embodiment, in addition that a composition range of the main component is controlled in the above range, all of the above tin oxide, bismuth oxide, and cobalt oxide are always included as the sub component. As a result, it is possible to decrease sintering temperature and use a metal such as Ag having a relatively low melting point as an integrally fired inner conductor. Further, a ferrite sintered body sintered at low temperature maintains a characteristic where Q value is high.

(19) Note that, with respect to tin oxide, bismuth oxide, and cobalt oxide, when any one or more thereof is not included, the above effects cannot be obtained adequately. That is, it is considered that the above effects are composite effects which can be obtained only when tin oxide, bismuth oxide, and cobalt oxide are included by a certain amount at the same time.

(20) Also, in the ferrite composition according to the present embodiment, in addition to the above sub component, additional components such as manganese oxide like Mn.sub.3O.sub.4, zirconium oxide, and glass compound may be further included in a range where the effects of the present invention are not disturbed. A content of the additional components is not particularly limited, and it is approximately 0.05 to 1.0 wt %, for example.

(21) Further, the ferrite composition according to the present embodiment may include an oxide of inevitable impurity element.

(22) Specifically, as the inevitable impurity element, C, S, Si, Cl, As, Se, Br, Te and I, a typical metal element such as Li, Na, Mg, Al, Ca, Ga, Ge, Sr, Cd, In, Sb, Ba and Pb, and a transition metal element such as Sc, Ti, V, Cr, Y, Nb, Mo, Pd, Ag, Hf and Ta are exemplified. Also, the oxide of the inevitable impurity element may be included in the ferrite composition as far as the content thereof is approximately 0.05 wt % or less.

(23) The ferrite composition according to the present embodiment has ferrite particles and crystal grain boundaries present among adjacent crystal particles. An average crystal particle diameter of the crystal particles is preferably 0.2 to 1.5 m.

(24) Next, an example of a method for manufacturing the ferrite composition according to the present embodiment will be described. First, starting materials (a material of the main component and a material of the sub component) are mixed after they are weighted so as to satisfy a predetermined composition ratio, and a raw material mixture is obtained. As a mixing method, for example, wet mixing using a ball mill and dry mixing using a dry mixer can be raised, Note that, it is preferable to use a starting material having an average particle diameter of 0.05 to 1.0 m.

(25) As a material of the main component, iron oxide (-Fe.sub.2O.sub.3), copper oxide (CuO), nickel oxide (NiO), zinc oxide (ZnO) if necessary, or composite oxide etc. can be used. Further, other various compounds to become the above oxides and composite oxides after firing can be used. As examples to become the above oxides after firing, a metal alone, carbonate, oxalate, nitrate, hydroxide, halogenide, and organometallic compound etc. can be exemplified.

(26) As a material of the sub component, tin oxide, bismuth oxide, and cobalt oxide can be used. The oxide to become the material of the sub component is not particularly limited, and a composite oxide or so can be used. Further, other various compounds to become the above oxides and composite oxides after firing can be used. As examples to become the above oxides after firing, a metal alone, carbonate, oxalate, nitrate, hydroxide, halogenide, and organometallic compound etc. can be exemplified.

(27) Note that, Co.sub.3O.sub.4, which is an example of cobalt oxide, is preferable as a material of cobalt oxide. This is because it is easy to store and handle and valence thereof is stable even in the air.

(28) Next, the raw material mixture is calcined and a calcined material is obtained. Calcination is performed so as to induce thermal decomposition of the raw material, homogeneity of components, generation of the ferrite, disappearance of ultrafine powder by sintering, and particle growth to a proper particle size and to convert the raw material mixture to a form suitable for the following process. Such a calcination is preferably performed at a temperature of 650 to 750 C. for 2 to 15 hours in general. Calcination is usually performed under the atmosphere (air), but it may be performed under an atmosphere where an oxygen partial pressure is lower than that of the atmosphere. Note that, the mixing of the material of the main component and the material of the sub component may be performed before the calcination or after it.

(29) Next, the calcined material is pulverized to obtain a pulverized material. Pulverization is performed to disconnect an aggregation so that the calcined material becomes powders having a proper sinterability. When the calcined material forms large lumps, wet pulverization is performed by using a ball mill or an attritor etc. after performing coarse pulverization. The wet pulverization is performed until an average particle diameter of the pulverized material becomes preferably 0.1 to 1.0 m or so.

(30) By using the obtained pulverized material, a multilayer inductor according to the present embodiment is manufactured. A method for manufacturing the multilayer inductor is not limited, but hereinafter, a sheet method is used.

(31) First, the obtained pulverized material is slurried with an additive such as solvent and binder, and a paste is produced. Then, green sheets are formed by using the paste. Next, through transforming the formed green sheets to a predetermined shape and performing a debinding step and a firing step, the multilayer inductor according to the present embodiment is obtained. The firing is performed at a temperature which is the same or lower than the melting point of the coil conductor 5 and the leading electrodes 5a and 5b. For example, when the coil conductor 5 and the leading electrodes 5a and 5b are Ag (melting point: 962 C.), the firing is preferably performed at 850 to 920 C. The firing is usually performed for 1 to 5 hours or so. Also, the firing may be performed in the atmosphere (air) or may be performed under an atmosphere where an oxygen partial pressure is lower than that of the atmosphere. The multilayer inductor obtained as this way is comprised of the ferrite composition according to the present embodiment.

(32) Up to here, the embodiment of the present invention was described, but the present invention is not limited to the embodiment. Needless to say, the present invention can be performed by various embodiments in a range where the points of the present invention are not deviated. For example, as the ferrite layers 4 of the LC composite electronic component 10 shown in FIG. 2, the ferrite composition of the present invention may be used. Note that, in FIG. 2, a part shown by sign 12 is an inductor part, and a part shown by sign 14 is a capacitor part.

(33) Hereinafter, the present invention will be described based on more detailed examples, but the present invention is not limited to the examples.

EXAMPLE 1

(34) First, as materials of the main component, Fe.sub.2O.sub.3, NiO, CuO, and ZuO (when zinc oxide was included) were prepared. As materials of the sub component, SnO.sub.2, Bi.sub.2O.sub.3, and Co.sub.3O.sub.4 were prepared.

(35) Next, after powders of the prepared main component and sub component were weighted so that they satisfied the composition described in Tables 1 and 2 as sintered bodies, they were wet mixed for 16 hours in a ball mill, and a raw material mixture was obtained.

(36) Next, after the obtained raw material mixture was dried, it was calcined for 4 hours at 720 C. in the air, and the calcined powders were obtained. The pulverized powders were obtained by wet pulverizing the calcined powders for 16 hours in a steel ball mill.

(37) Next, after drying the pulverized powders, granulation was performed by adding 10.0 wt % of a polyvinyl alcohol solution as a binder having 6 wt % concentration into the pulverized powder 100 wt % so as to obtain granules. The granules were molded by pressure so as to satisfy a molding density of 3.20 Mg/m.sup.3, and toroidal-shaped (size=outer diameter 13 mminner diameter 6 mmheight 3 mm) molded bodies were obtained.

(38) Next, each of the molded bodies were fired for 2 hours at 900 C., which is below the melting point of Ag (962 C.), in the air. Then, toroidal core samples as sintered bodies were obtained. Further, the following characteristic evaluations were performed on the samples.

(39) Sintered Density

(40) With respect to the obtained toroidal core samples, a sintered density was calculated from a size and weight of the sintered body after firing. In the present example, a sintered density of 5.0 Mg/m.sup.3 or more was considered as good. Also, with respect to samples having a sintered density of less than 5.0 Mg/m.sup.3, the following characteristic evaluations were omitted because other characteristic evaluations were considered as not worthy of being performed.

(41) Curie Temperature

(42) A curie temperature was measured based on JIS-C-2560-1. In the present example, the evaluations were performed by whether the Curie temperature was 125 C. or higher. With respect to samples whose Curie temperature was less than 125 C., the following characteristic evaluations were omitted because other characteristic evaluations were considered as not worthy of being performed due to inconvenience in an operating temperature of the inductor.

(43) Permeability and Q Value

(44) With respect to samples having good sintered density and Curie temperature, primary and secondary sides thereof were wound by copper wire with 20 turns and 7 turns, respectively. Permeability and Q values were measured by using B-H Analyzer (IWATSU TEST INSTRUMENTS CORPORATION, B-H ANALYZER SY-8218) and AMPLIFIER (NF CORPORATION, HIGH SPEED BIPORLAR AMPLIFIER HSA 4101-IW). As the measuring conditions, measuring frequency was 1 MHz, measuring temperature was 25 C., and external magnetic fields were applied by 100 A/m and 200 A/m.

(45) In the present example, it is preferable that Q value is 110 or higher in the external magnetic field 100 A/m. Further, it is preferable that Q value is 55 or higher in the external magnetic field 200 A/m. The above results are shown in Table 1 (Example) and Table 2 (Comparative Example). Also, samples where cells of Curie temperature show represent that Curie temperature is 125 C. or higher, and the sample where the cell of Curie temperature shows x represents that Curie temperature is less than 125 C.

(46) TABLE-US-00001 TABLE 1 Sintered Main Component Sub Component Density Sample (mol %) (wt %) (Mg/m.sup.3) Curie Q Q Number Fe.sub.2O.sub.3 CuO ZnO SnO.sub.2 Bi.sub.2O.sub.3 Co.sub.3O.sub.4 900 C. Temperature at 100 A/m at 100 A/m at 200 A/m at 200 A/m 1 48.0 9.0 18.0 0.5 0.10 0.80 5.27 102 123 107 56 2 48.0 9.0 18.0 0.5 0.50 1.50 5.23 87 132 90 60 3 48.5 9.0 18.0 0.8 0.10 0.80 5.10 99 126 102 62 4 47.0 10.0 7.0 1.5 0.70 0.23 5.13 39 168 39 124 5 47.0 9.0 18.0 1.8 1.00 1.80 5.24 67 129 68 88 6 47.0 9.0 18.0 2.0 0.30 0.24 5.16 83 150 87 96 7 47.0 9.0 18.0 2.4 0.20 0.80 5.00 71 153 72 95 8 47.0 9.0 18.0 2.4 0.28 0.80 5.10 75 163 79 84 9 47.0 9.0 18.0 2.5 0.50 0.30 5.26 73 158 75 92 10 43.0 9.0 25.0 4.0 0.70 1.00 5.22 58 137 60 93 11 47.0 9.0 18.0 4.0 1.00 0.50 5.00 66 142 69 84 12 47.0 9.0 20.0 2.0 0.31 0.21 5.23 81 151 85 67 13 46.0 9.0 26.0 2.0 0.30 0.25 5.14 81 180 84 96 14 46.0 9.0 26.0 1.8 0.30 0.50 5.11 73 184 76 90 15 46.0 9.0 26.0 1.0 0.30 0.85 5.12 65 193 67 120 16 46.0 9.0 26.0 1.0 0.30 1.20 5.04 50 176 53 95 17 46.0 9.0 26.0 1.0 0.30 2.00 5.00 42 168 46 116 18 43.0 9.0 18.0 1.5 0.80 3.00 5.03 21 124 21 104 19 40.0 9.0 18.0 1.5 0.30 0.23 5.21 58 174 61 110 20 42.0 9.0 18.0 1.5 0.30 1.00 5.20 47 163 48 132 21 49.0 12.0 18.0 1.0 0.30 1.00 5.24 96 134 99 78 22 49.8 9.0 18.0 0.8 0.30 0.50 5.31 94 125 101 59 23 48.0 5.0 25.0 1.5 0.30 0.80 5.02 74 165 77 96 24 48.0 14.0 25.0 1.5 0.30 0.80 5.21 82 184 86 93 25 45.0 9.0 0.0 2.0 0.30 0.40 5.27 12 126 12 109 26 47.0 9.0 0.5 1.5 0.30 0.23 5.23 25 185 26 149 27 45.0 7.0 3.0 1.5 0.30 0.23 5.00 32 163 37 122 28 47.0 10.0 7.0 1.5 0.40 0.23 5.24 41 178 42 113 29 47.0 9.0 30.0 1.5 0.50 1.00 5.21 128 110 132 55 30 45.0 9.0 32.0 1.5 0.30 1.50 5.12 119 113 125 58

(47) TABLE-US-00002 TABLE 2 Sintered Main Component Sub Component Density Sample (mol %) (wt %) (Mg/m.sup.3) Curie Q Q Number FeO.sub.3 CuO ZnO SnO.sub.2 Bi.sub.2O.sub.3 Co.sub.3O.sub.4 900 C. Temperature at 100 A/m at 100 A/m at 200 A/m at 200 A/m 31 47.0 9.0 10.0 0.00 0.00 0.00 5.28 65 36 71 18 32 47.0 9.0 15.0 0.00 0.00 0.50 5.18 86 109 90 45 33 47.0 9.0 18.0 2.0 0.20 0.00 5.16 85 57 88 31 41 47.0 9.0 18.0 0.1 0.28 0.40 5.28 100 98 112 41 42 47.0 9.0 18.0 5.0 0.30 0.24 4.60 43 47.0 9.0 18.0 2.5 0.03 0.24 4.70 44 48.5 9.0 18.0 0.8 1.50 0.80 5.29 124 69 139 22 45 47.0 9.0 18.0 1.5 0.30 0.02 5.32 84 58 91 28 46 47.0 9.0 18.0 1.5 0.20 0.20 5.16 83 90 85 48 51 35.0 9.0 18.0 1.5 0.30 0.23 5.24 38 80 39 42 52 50.0 9.0 18.0 1.5 0.30 0.23 4.10 53 48.0 4.0 18.0 1.5 0.30 0.23 4.83 54 48.0 18.0 18.0 1.5 0.30 0.23 5.12 78 86 85 38 55 47.0 9.0 41.0 1.5 0.30 0.23 5.25 X

(48) From Table 1 and Table 2, it was confirmed that Q values were good when three kinds of SnO.sub.2, Bi.sub.2O.sub.3 and Co.sub.3O.sub.4 as the sub component were included, and when the contents of the main component and the sub component were in a range of the present invention (sample numbers: 1 to 30). On the other hand, when either the main component or the sub component was out of the range of the present invention (sample numbers: 31 to 55), sintered bodies whose any one or more of sintered density, Curie temperature, and Q value was out of the excellent range were obtained.

(49) Further, FIG. 3 (H=100 A/m) and FIG. 4 (H=200 A/m) represent that the results of Table 1 and Table 2 were graphed by every external magnetic field. According to FIG. 3 and FIG. 4, it is clear that Q values of Example are higher than those of Comparative Example when samples of Example and Comparative Example whose is close are compared.

EXAMPLE 2

(50) With respect to sample number 12 of Table 1 and sample numbers 31, 32 and 33 of Table 2, FIG. 5 was obtained by summarizing the results of Q values measured under an external magnetic field (H=20 to 400 A/m) except for H=100 A/m and H=200 A/m. Other factors other than the external magnetic field were measured in the same way as with Example 1. Note that, sample number 31 corresponds to a conventional non-additive material, sample number 32 corresponds to a conventional Co additive material, and sample number 33 corresponds to a conventional SnBi additive material. Also, with respect to the conventional non-additive material and Co additive material, Q values could not be measured at H=350 and 400 A/m.

(51) From FIG. 5, it is understood that the SnCoBi additive material according to the present invention can keep Q values high under the high magnetic fields of 20 to 400 A/m compared with the conventional non-additive material, Co additive material, and SnBi additive material.

(52) As the above, the ferrite material according to the present invention can be sintered at a temperature lower than the melting point of Ag (962 C.). Further, the sintered body obtained by sintering the ferrite material according to the present invention at a low temperature has a high characteristic even under high electric currents. Therefore, by using the ferrite material according to the present invention, it is possible to obtain electronic components which can be downsized and further are effective for even large amplitude signals.

NUMERICAL REFERENCES

(53) 1 . . . multilayer inductor 2 . . . element 3 . . . terminal electrode 4 . . . multilayer body 5 . . . coil conductor 5a, 5b . . . leading electrode 10 . . . LC composite electronic component 12 . . . inductor part 14 . . . capacitor part