Abstract:
A sixth coil electrode forming a first coil is electrically connected to a twelfth coil electrode forming a second coil, for example, via a second capacitor electrode in a second capacitor electrode layer. Thus, an induction body has a permeability significantly smaller than the permeability of a magnetic body (for example permeability μ=1). Accordingly, it is possible to minimize the permeability to such a degree that it is possible to ignore the connection between the first coil and the second coil appearing equivalently and to obtain a desired frequency characteristic.

Description:
TECHNICAL FIELD 
     The present invention relates to an electronic part having a base member formed by joining a dielectric portion and a magnetic portion. The present invention relates to an electronic part which is preferably usable, for example, for an LC filter. 
     BACKGROUND OF THE INVENTION 
     In recent years, an FM radio receiver and/or an FM transmitter may be carried on a portable device (including an electronic device) such as a mobile phone. In this case, it is necessary for the portable device to provide a filter which allows a signal in the FM band to pass therethrough in addition to a filter which allows a signal in the ordinarily used frequency band to pass therethrough. 
     A dielectric filter has been hitherto used as the filter which allows the signal in the FM band to pass therethrough. 
     The conventional dielectric filter includes, for example, a filter disclosed, for example, in Patent Document 1. However, this filter is provided in order to attenuate the spurious at a level of 500 MHz. It is true that a signal at 76 to 108 MHz including the FM band is allowed to pass the filter. However, the filter is not for attenuating the signal in the high frequency band, for example, at 800 MHz, 1.4 GHz, 1.9 GHz, 2.5 GHz, and 5 GHz as the frequency band ordinarily used by a portable device. 
     Therefore, it is obvious that the noise in the high frequency band cannot be suppressed when the FM radio receiver and/or the FM transmitter is carried on the portable device. 
     As for the value of the inductance required for the filter, the lower the frequency is, the larger the required value is. When a coil is formed with a filter having a passband in the vicinity of 100 MHz, it is necessary to increase the number of turns and/or increase the size of the coil in order to obtain the required inductance. 
     The required inductance is obtained by increasing the number of turns of the coil. However, because the conductor resistance of the coil is increased, the Q characteristic is consequently deteriorated, failing to obtain suitable filter characteristic. Further, because stray components disadvantageously appear, and suitable attenuation characteristic is not obtained. Furthermore, because the area of the coil is increased, it is impossible to realize a compact size. By contrast, the portable device on which the filer is carried is required to be compact in size. In relation thereto, the dimension of the conventional filter is so large, i.e., 4.8 mm×3.5 mm, that it is not usable for the portable device. 
     In the conventional technique, a stacked type electronic part which has a base member obtained by joining a dielectric layer and a magnetic layer (see, for example, Patent Document 2) has been proposed. However, the stacked type electronic part is provided only to suppress warpage, delamination, and cracks in the product by adding a dummy layer. It is unclear whether or not the stacked type electronic part makes it possible to carry the FM radio receiver and/or the FM transmitter on the portable device. 
     Patent Document 1: Japanese Patent No. 2505135; 
     Patent Document 2: Japanese Laid-Open Patent Publication No. 2003-37022. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an electronic part which makes it possible to realize a compact size of the electronic part, to improve the characteristic thereof, and to carry an FM radio receiver and/or an FM transmitter, for example, on a portable device, by improving the stacked type electronic part having the base member obtained by joining the dielectric layer and the magnetic layer as described above. 
     According to the present invention, there is provided an electronic part comprising a base member which is constructed by joining a dielectric portion and a magnetic portion; a plurality of capacitor electrodes which are formed in the dielectric portion of the base member; and a plurality of coil electrodes which are formed in the magnetic portion of the base member; wherein one coil electrode and the other coil electrode are electrically connected to one another via one capacitor electrode. 
     For example, when two coils are electrically connected to one another, one coil electrode (end of one coil) and the other coil electrode (end of the other coil) are usually connected electrically to one another in a magnetic portion. 
     However, in this case, positive coupling is equivalently formed between the two coils. Therefore, when such an electronic part is used as a filter, the passband of the filter may undesirably be narrowed, making it impossible to obtain desired frequency characteristic. 
     On the other hand, in the present invention, one coil electrode and the other coil electrode, which are formed in the magnetic portion, are electrically connected to one another via one capacitor electrode which is formed in the dielectric portion. Therefore, it is possible to decrease the coupling formed equivalently between the two coils to such an extent that the coupling is negligible. It is possible to obtain the desired frequency characteristic. 
     In another aspect, according to the present invention, there is provided an electronic part comprising a base member which is constructed by joining a dielectric portion and a magnetic portion; at least one ground electrode which is formed in the dielectric portion of the base member; a plurality of capacitor electrodes which are formed in the dielectric portion of the base member; and a plurality of coil electrodes which are formed in the magnetic portion of the base member; wherein the ground electrode and at least a first capacitor electrode among the plurality of capacitor electrodes are formed on a first formation surface of the dielectric portion respectively; at least second and third capacitor electrodes among the plurality of capacitor electrodes are formed on a second formation surface of the dielectric portion respectively; the ground electrode is opposed to the second capacitor electrode; and the second capacitor electrode and the third capacitor electrode are opposed to the first capacitor electrode. 
     For example, assuming that the ground capacitance is formed between one capacitor electrode and a ground electrode, and the capacitor different from the ground capacitance is formed by the other two capacitor electrodes. On this assumption, if the ground electrode is formed to have a wide width, the ground electrode is opposed to the three capacitor electrodes. As a result, stray capacitance appears in relation to the ground electrode. The high frequency attenuation characteristic may undesirably be deteriorated. 
     On the other hand, in the present invention, the first capacitor electrode and the ground electrode are formed on the first formation surface of the dielectric portion respectively, the second capacitor electrode and the third capacitor electrode are formed on the second formation surface of the dielectric portion respectively, the ground electrode is opposed to the second capacitor electrode, and the second capacitor electrode and the third capacitor electrode are opposed to the first capacitor electrode. Therefore, stray capacitance does not appear in relation to the ground electrode. It is possible to suppress the deterioration of the high frequency attenuation characteristic. 
     When the combination as described above is regarded as one arrangement, it is possible to increase the ground capacitance and the capacitance of the capacitor by aligning the arrangements in the stacking direction of dielectric layers in the dielectric portion. It is possible to further improve the high frequency attenuation characteristic. 
     As explained above, according to the electronic part concerning the present invention, it is possible to miniaturize the electronic part and improve the characteristics. For example, the electronic part makes it possible to carry an FM radio receiver and/or an FM transmitter on a portable device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram illustrating a filter according to an embodiment of the present invention; 
         FIG. 2  is a perspective view illustrating an appearance of the filter according to the embodiment of the present invention; 
         FIG. 3  is an exploded perspective view illustrating a filter according to a first embodiment; 
         FIG. 4  is a perspective view illustrating an example of ordinary electric connection in relation to a first coil and a second coil; 
         FIGS. 5A and 5B  are views showing the function brought about by the example connection shown in  FIG. 4 ; 
         FIG. 6  is a perspective view illustrating an example of electric connection in relation to a first coil and a second coil in the filter according to the first embodiment; 
         FIG. 7  is a view showing the function brought about by the example shown in  FIG. 6 ; 
         FIG. 8  is a view showing an example of ordinary stacking of electrodes for forming first to third capacitors and the function thereof; 
         FIG. 9  is a view showing an example of stacking of electrodes for forming first to third capacitors and the function thereof in the filter according to the first embodiment; 
         FIG. 10  is a table illustrating results of a first experimental example in relation to a filter concerning a second embodiment (measurement of the dielectric characteristic when base members are manufactured by changing the composition (x, y 1 , y 2 , and z) in xBaO.y 1 Nd 2 O 3 .y 2 Bi 2 O 3 .zTiO 2 ; 
         FIG. 11  is a table illustrating preferred Examples of dielectric materials for constructing the joint portion; 
         FIG. 12  is a table illustrating results of a second experimental example in relation to the filter concerning the second embodiment (measurement of the initial magnetic permeability and the high frequency characteristic when base members are manufactured with different composition of NiO, ZnO, Fe 2 O 3 , Co 3 O 4 , and CuO); 
         FIG. 13  is a graph illustrating results of Example 24 and Comparative Examples 14 and 15 in a third experimental example in relation to the filter of the second embodiment (change of Q with respect to the frequency (1 to 1,000 MHz) concerning the selection of the composition of ZnO and Co 3 O 4 ); 
         FIG. 14  is a graph illustrating results of Example 24 and Comparative Examples 14 and 15 in a fourth experimental example in relation to the filter concerning the second embodiment (change of the inductance value with respect to the frequency (1 to 1,000 MHz) concerning the selection of the composition of ZnO and Co 3 O 4 ); 
         FIG. 15  is a graph illustrating results of Comparative Examples 14 and 16 in the third experimental example; 
         FIG. 16  is a graph illustrating results of Comparative Examples 14 and 16 in the fourth experimental example; 
         FIG. 17  is a view showing attenuation characteristic (0 to 2 GHz) of the filter of the second embodiment and a filter (conventional example) composed of a base member of a dielectric material; 
         FIG. 18  is a view showing attenuation characteristic (0 to 6 GHz) of the filter concerning the second embodiment; 
         FIG. 19  is a view showing insertion loss characteristic of the filter of the second embodiment and a filter (conventional example) composed of a base member of a dielectric material; 
         FIG. 20  is a view showing the characteristics illustrating the change of the high frequency characteristic and the temperature coefficient with respect to the amount of Co 3 O 4  added in a fifth experimental example; 
         FIG. 21  is a view illustrating the change of the high frequency characteristic and the temperature coefficient with respect to the amount of ZnO added in the fifth experimental example; 
         FIG. 22  is a view illustrating the change of the high frequency characteristic and the temperature coefficient with respect to the amount of Fe 2 O 3  added in the fifth experimental example; 
         FIG. 23  is a view illustrating the change of the high frequency characteristic and the temperature coefficient with respect to the amount of NiO added in the fifth experimental example; and 
         FIG. 24  is a table illustrating results of a sixth experimental example in relation to the filter of the third embodiment (measurement of the initial magnetic permeability, the temperature coefficient, and the high frequency characteristic when base members are manufactured with different composition of NiO, ZnO, Fe 2 O 3 , Co 3 O 4 , and CuO). 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An explanation will be made below with reference to  FIGS. 1 to 24  showing embodiments in which the electronic part according to the present invention is applied, for example, to a filter for an FM radio receiver and/or an FM transmitter. 
     As shown in  FIG. 1 , a filter  10  according to this embodiment basically has a circuit structure in which a first capacitor C 1  and a first coil L 1  are connected in parallel between an input terminal  12  and the ground, a second capacitor C 2  and a third capacitor C 3  are connected in series between the input terminal  12  and an output terminal  14 , and a second coil L 2  is connected in parallel to both ends of the second capacitor C 2 . 
     Specifically, as shown in  FIG. 2 , a base member  16  is provided. The base member  16  is formed by sintering and integrating a dielectric portion  18 , a magnetic portion  20 , a joint portion  22  which joins the dielectric portion  18  and the magnetic portion  20 , and a dummy portion  24  which is joined to a lower portion of the magnetic portion  20 . 
     The dummy portion  24  is formed in order to suppress warpage, delamination, and cracks in the base member  16  as described in Patent Document 2 as well. Reference may be made to Patent Document 2 in relation to, for example, the selection of materials. 
     Three embodiments will now be explained with reference to  FIGS. 3 to 24  about the filter  10  according to this embodiment. 
     At first, a filter  10 A according to a first embodiment will be explained with reference to  FIGS. 1 to 9 . 
     As shown in  FIG. 3 , in the filter  10 A according to the first embodiment, the dielectric portion  18  is constructed by stacking a plurality of dielectric layers. In detail, there are provided a first dummy layer Sa 1 , a second dummy layer Sa 2 , first to fourth capacitor electrode layers Sb 1  to Sb 4 , and a third dummy layer Sa 3  in this order from the top. Each of the first dummy layer Sa 1 , the second dummy layer Sa 2 , the first to fourth capacitor electrode layers Sb 1  to Sb 4 , and the third dummy layer Sa 3  is constructed by one layer or a plurality of layers. 
     The magnetic portion  20  is constructed by stacking a plurality of magnetic layers. In detail, there are provided first to fourth dummy layers Sc 1  to Sc 4 , first to sixth coil electrode layers Sd 1  to Sd 6 , and fifth to seventh dummy layers Sc 5  to Sc 7  in this order from the top. Each of the first to fourth dummy layers Sc 1  to Sc 4 , the first to sixth coil electrode layers Sd 1  to Sd 6 , and the fifth to seventh dummy layers Sc 5  to Sc 7  is constructed by one layer or a plurality of layers. 
     The joint portion  22  is constructed by one intermediate layer Se. The intermediate layer Se is constructed by one layer or a plurality of layers. 
     The dummy portion  24  is constructed by one dummy layer Sf. The dummy layer Sf is constructed by one layer or a plurality of layers. 
     Each of the first to third dummy layers Sa 1  to Sa 3  of the dielectric portion  18  and the first to seventh dummy layers Sc 1  to Sc 7  of the magnetic portion  20  is formed in order to suppress the occurrence of any warpage, any delamination, and any crack of the base member  16  in the same manner as in the dummy portion  24 . 
     As shown in  FIG. 2 , the input terminal  12 , a ground terminal  26 , and the output terminal  14  are formed on a first side surface  16   a  of the base member  16 . A first connecting terminal  28   a , a second connecting terminal  28   b , and an NC (Non-connection) terminal  30  are formed on a second side surface  16   b  (side surface opposite to the first side surface  16   a ) of the base member  16 . 
     As shown in  FIG. 3 , various electrode layers are formed on the first to fourth capacitor electrode layers Sb 1  to Sb 4  and the first to sixth coil electrode layers Sd 1  to Sd 6 . Details thereof will be explained below. At first, a first ground electrode  32  having one end connected to the ground terminal  26 , and a first capacitor electrode  34  having one end connected to the first connecting terminal  28   a  are formed on a principal surface of the first capacitor electrode layer Sb 1 . The first capacitor electrode  34  has a protruding portion  34   a  which protrudes toward the first ground electrode  32 . 
     A second capacitor electrode  36  having one end connected to the input terminal  12  and the other end connected to the second connecting terminal  28   b , and a third capacitor electrode  38  having one end connected to the output terminal  14  are formed on a principal surface of the second capacitor electrode layer Sb 2 . The second capacitor electrode  36  has a protruding portion  36   a  which protrudes toward the third capacitor electrode  38 . 
     A second ground electrode  40  and a fourth capacitor electrode  42 , which are similar to the first ground electrode  32  and the first capacitor electrode  34  formed on the first capacitor electrode layer Sb 1 , are formed on a principal surface of the third capacitor electrode layer Sb 3 . The fourth capacitor electrode  42  has a protruding portion  42   a  which protrudes toward the second ground electrode  40 . 
     A fifth capacitor electrode  44  and a sixth capacitor electrode  46 , which are similar to the second capacitor electrode  36  and the third capacitor electrode  38  formed on the second capacitor electrode layer Sb 2 , are formed on a principal surface of the fourth capacitor electrode layer Sb 4 . The fifth capacitor electrode  44  has a protruding portion  44   a  which protrudes toward the sixth capacitor electrode  46 . 
     On the other hand, first to sixth coil electrodes  50   a  to  50   f  for forming the first coil L 1  respectively and seventh to twelfth coil electrodes  52   a  to  52   f  for forming the second coil L 2  respectively are formed on respective principal surfaces of the first to sixth coil electrode layers Sd 1  to Sd 6 . The first coil electrode  50   a , which is formed on the principal surface of the first coil electrode layer Sd 1 , has one end which is connected to the ground terminal  26 . The seventh coil electrode  52   a  has one end which is connected to the first connecting terminal  28   a . The sixth coil electrode  50   f , which is formed on the principal surface of the sixth coil electrode layer Sd 6 , has one end which is connected to the input terminal  12 . The twelfth coil electrode  52   f  has one end which is connected to the second connecting terminal  28   b . Further, the first to sixth coil electrodes  50   a  to  50   f  are electrically connected to one another via via-holes respectively. The seventh to twelfth coil electrodes  52   a  to  52   f  are electrically connected to one another via via-holes respectively. 
     With this structure, the first capacitor C 1  shown in  FIG. 1  is formed by the combined capacitance of the capacitance formed by the first ground electrode  32  and the second capacitor electrode  36  opposed to the first ground electrode  32 , the capacitance formed by the second ground electrode  40  and the second capacitor electrode  36  opposed to the second ground electrode  40 , and the capacitance formed by the second ground electrode  40  and the fifth capacitor electrode  44  opposed to the second ground electrode  40 . 
     Similarly, the second capacitor C 2  shown in  FIG. 1  is a combined capacitance of the capacitance formed by the protruding portion  34   a  of the first capacitor electrode  34  and the protruding portion  36   a  of the second capacitor electrode  36  opposed to the protruding portion  34   a , the capacitance formed by the protruding portion  36   a  of the second capacitor electrode  36  and the protruding portion  42   a  of the fourth capacitor electrode  42  opposed to the protruding portion  36   a , and the capacitance formed by the protruding portion  42   a  of the fourth capacitor electrode  42  and the protruding portion  44   a  of the fifth capacitor electrode  44  opposed to the protruding portion  42   a.    
     Further, the third capacitor C 3  shown in  FIG. 1  is a combined capacitance of the capacitance formed by the first capacitor electrode  34  and the third capacitor electrode  38  opposed to the first capacitor electrode  34 , the capacitance formed by the third capacitor electrode  38  and the fourth capacitor electrode  42  opposed to the third capacitor electrode  38 , and the capacitance formed by the fourth capacitor electrode  42  and the sixth capacitor electrode  46  opposed to the fourth capacitor electrode  42 . 
     The first coil L 1  shown in  FIG. 1  is formed by the first to sixth coil electrodes  50   a  to  50   f . The second coil L 2  shown in  FIG. 1  is formed by the seventh to twelfth coil electrodes  52   a  to  52   f . In particular, in the first embodiment, the first coil electrode  50   a  is electrically connected to the twelfth coil electrode  52   f  via the input terminal  12 , the second capacitor electrode  36 , the fifth capacitor electrode  44 , and the second connecting terminal  28   b.    
     For example, when the first coil L 1  and the second coil L 2  are electrically connected to one another, the following arrangement is conceived as shown in  FIG. 4 . That is, the sixth coil electrode  50   f  for forming the first coil L 1  and the twelfth coil electrode  52   f  for forming the second coil L 2  are electrically connected to one another via a lead electrode  54  in the magnetic portion  20 . 
     However, in this case, when viewed equivalently as shown in  FIG. 5A , a third coil L 12  is connected between the input terminal  12  and the connection point  56  of the first coil L 1  and the second coil L 2 . As a result, the first coil L 1  and the second coil L 2  are positively coupled as shown in  FIG. 5B . Therefore, when this electronic part is used as a filter, because the passband of the filter may undesirably be narrowed, it is impossible to obtain any desired frequency characteristic. 
     On the other hand, in the case of the filter  10 A according to the first embodiment, as partially shown in  FIG. 6 , the sixth coil electrode  50   f  for forming the first coil L 1  and the twelfth coil electrode  52   f  for forming the second coil L 2  are electrically connected to one another, for example, via the second capacitor electrode  36  formed on the second capacitor electrode layer Sb 2 . Therefore, as shown in  FIG. 7 , the magnetic permeability of the dielectric portion  18  is significantly smaller than the magnetic permeability of the magnetic portion  20  (for example, magnetic permeability μ=1). Therefore, the coupling between the first coil L 1  and the L 2 , which can be shown in the equivalent circuit, can be decreased to such an extent that the coupling between the first coil L 1  and the L 2  is negligible. It is possible to obtain the desired frequency characteristic. 
     When the first to third capacitors C 1  to C 3  shown in  FIG. 1  are formed, as shown in  FIG. 8 , for example, a ground electrode  60  is formed on the substantially entire principal surface of the first dielectric layer, a first electrode  62  and a second electrode  64  are formed on the principal surface of the second dielectric layer, and a third electrode  66  is formed on the principal surface of the third dielectric layer. In this case, a first capacitor C 1  is formed between the ground electrode  60  and the first electrode  62 , a second capacitor C 2  is formed between the first electrode  62  and the third electrode  66 , and a third capacitor C 3  is formed between the second electrode  64  and the third electrode  66 . 
     However, when the ground electrode  60  is wide, the ground electrode  60  is also opposed to the two electrodes (second electrode  64  and third electrode  66 ) which do not relate to the formation of the first capacitor C 1 . As a result, stray capacitances Cs 1 , Cs 2  are generated between the ground electrode  60  and the second electrode  64  and between the ground electrode  60  and the third electrode  66  respectively. The high frequency attenuation characteristic may undesirably be deteriorated. 
     On the other hand, in the case of the filter  10 A according to the first embodiment, as partially shown in  FIG. 9 , the first ground electrode  32  and the first capacitor electrode  34  are formed on the first capacitor electrode layer Sb 1  of the dielectric portion  18  respectively. The second capacitor electrode  36  and the third capacitor electrode  38  are formed on the second capacitor electrode layer Sb 2  respectively. The first ground electrode  32  and the second capacitor electrode  36  are opposed to one another. The second capacitor electrode  36  and the third capacitor electrode  38  are opposed to the first capacitor electrode  34 . Therefore, the first ground electrode  32  is not opposed to the two electrodes (first capacitor electrode  34  and third capacitor electrode  38 ) which do not relate to the formation of the first capacitor C 1 . As a result, no stray capacitance appears between the first ground electrode  32  and the first capacitor electrode  34  and between the first ground electrode  32  and the third capacitor electrode  38  respectively. It is possible to suppress the deterioration of the high frequency attenuation characteristic. 
     Further, when the combination shown in  FIG. 9  is regarded as one arrangement, the two arrangements are aligned in the stacking direction of the dielectric layers in the dielectric portion  18  in the filter  10 A according to the first embodiment shown in  FIG. 3 . Therefore, it is possible to increase the respective capacitances of the first to third capacitors C 1  to C 3 . It is possible to further improve the high frequency attenuation characteristic. Of course, it is also allowable to stack three or more of the arrangements. 
     Next, a filter  10 B according to a second embodiment will be explained with reference to  FIGS. 10 to 19 . 
     In the filter  10 B according to the second embodiment, the materials are specified for the dielectric portion  18 , the magnetic portion  20 , and the joint portion  22  shown in  FIG. 2 . 
     Specifically, the dielectric material for forming the dielectric portion  18  contains a main component of a composition in xBaO.y 1 Nd 2 O 3 .y 2 Bi 2 O 3 .zTiO 2 , wherein
 
0.09≦x≦0.25,
 
0.05≦y 1 ≦0.20,
 
0&lt;y 2 ≦0.10, and
 
0.60≦z≦0.75.
 
     The reason thereof will be explained on the basis of results of a first experimental example shown in  FIG. 10  (Examples 1 to 13 and Comparative Examples 1 to 6). In the first experimental example, the dielectric characteristic is measured when the base member  16  is manufactured with different compositions (x, y 1 , y 2 , and z) in xBaO.y 1 Nd 2 O 3 .y 2 Bi 2 O 3 .zTiO 2 . The results are shown in  FIG. 10 . 
     In general, when the dielectric material has a high dielectric constant, the base member  16  is preferably miniaturized. However, according to the results shown in  FIG. 10 , it is preferable that the dielectric constant is not less than 60 and not more than 120. If the dielectric constant is less than 60, the effect of miniaturization is insufficient (see Comparative Example 1). If the dielectric constant exceeds 120, then the dimension is excessively decreased, the deficiency in the conductor printing arises, and the yield is lowered (see Comparative Examples 2 and 3). 
     It is preferable that the temperature coefficient (τ∈) of the dielectric constant is not more than 100 ppm/° C. as the absolute value as well. If the temperature coefficient exceeds this value, temperature adversely affects the operation at cold and hot places (see Comparative Examples 2 to 6). 
     The dielectric material, which satisfies the characteristics as described above, is preferably the dielectric having the composition of xBaO.y 1 Re 2 O 3 .y 2 Bi 2 O 3 .zTiO 2  (R: rare earth) in which the crystalline phase is of the pseudo-tungsten-bronze type. The composition is within the foregoing range. 
     In detail, if BaO is decreased, the dielectric constant is lowered. If BaO is excessively increased, the absolute value of the temperature coefficient is increased. If Bi 2 O 3  is lowered, then sintering at a low temperature is difficult, and the dielectric constant is lowered as well. If Bi 2 O 3  is excessively increased, the temperature coefficient is increased. If TiO 2  is increased, the dielectric constant is lowered. If TiO 2  is decreased, the temperature coefficient is increased. 
     In order to allow the sintering temperature to be in the vicinity of 900° C., about 0.1 to 5% by weight of glass may be added. The glass includes, for example, B 2 O 3 —SiO 2  based glass, ZnO—SiO 2 —B 2 O 3  based glass, and BaO—SiO 2 —B 2 O 3  based glass. 
     Half or less of Nd may be substituted with rare earth element such as La, Sm, and Pr. 
     Next, the dielectric material for forming the joint portion  22  is the BaO—TiO 2 —ZnO based dielectric. Specifically, it is preferable for aBaO, bZnO, and cTiO 2  to satisfy the following conditions:
 
4≦a≦45;
 
12≦b≦45; and
 
 a+b+c= 100.
 
     Preferred examples of compositions (Examples 14 to 18) are shown in  FIG. 11 . 
     With the composition in this range, it is possible to decrease the diffusion of the element between the magnetic portion  20  and the dielectric portion  18 , stabilize the junction. 
     The magnetic material for forming the magnetic portion  20  is ferrite having an initial magnetic permeability of not less than 10 at a frequency of not more than 150 MHz. 
     Specifically, it is preferable that the magnetic material is ferrite containing a main component of a composition in which NiO is 31 to 42 mol %, ZnO is 2 to 10 mol %, Fe 2 O 3  is 43 to 48 mol %, Co 3 O 4  is 0.5 to 3 mol %, and CuO is 10 to 14 mol %. 
     More preferably, the magnetic material is ferrite containing a main component of a composition in which NiO is 33 to 41 mol %, ZnO is 3 to 7 mol %, Fe 2 O 3  is 44 to 46 mol %, Co 3 O 4  is 1 to 3 mol %, and CuO is 11 to 13 mol %. 
     The reason thereof will be explained on the basis of results of a second experimental example shown in  FIG. 12  (Examples 19 to 27 and Comparative Examples 7 to 16). In the second experimental example, the initial magnetic permeability and the high frequency characteristic (frequency for Q=100) are measured when the base member  16  is manufactured by changing the composition for NiO, ZnO, Fe 2 O 3 , Co 3 O 4 , and CuO. The results are shown in  FIG. 12 . 
     If NiO is increased, then the high frequency characteristic (frequency for Q=100) is improved, but the initial magnetic permeability is lowered. Therefore, it is preferable that the lower limit of NiO is 31 mol %. If ZnO is increased, then the initial magnetic permeability is improved, but the high frequency characteristic is lowered. Therefore, the lower limit of ZnO is 2 mol %. Because the composition is determined to balance NiO and ZnO, the upper limits are determined respectively for the opposite reasons. 
     As for Fe 2 O 3 , because the composition is determined so that the crystalline structure of the magnetic portion is the spinel structure, the upper and lower limits are determined. This range is preferably 43 to 48 mol %. If the composition is outside this range, then hetero phase is formed so that the initial magnetic permeability and the high frequency characteristic are deteriorated. 
     Co 3 O 4  is added in order to improve the high frequency characteristic. If the amount of Co 3 O 4  added is less than 0.5 mol %, high frequency characteristic is not improved. If it exceeds 3 mol %, the initial magnetic permeability is inversely lowered. 
     CuO is added as a sintering aid in order to perform the sintering at about 900° C. If CuO is less than 10 mol %, sufficient density is not obtained by the sintering at 900° C. If CuO exceeds 14 mol %, then the sintering is excessively advanced, and pores appear from the inside. 
     An explanation will now be made with reference to  FIGS. 13 to 16  about two experimental examples (third and fourth experimental examples) for the selection of the compositions of ZnO and Co 3 O 4 . 
     In the third experimental example, the change of Q with respect to the frequency (1 to 1,000 MHz) is observed in Example 24 and Comparative Examples 14 to 16. Results are shown in  FIGS. 13 and 15 . 
     In the fourth experimental example, the change of the magnetic permeability (inductance) with respect to the frequency (1 to 1,000 MHz) is observed in Example 24 and Comparative Examples 14 to 16. Results are shown in  FIGS. 14 and 16 . 
     In  FIGS. 13 to 16 , the characteristic of Example 24 is indicated by the curve Ln 11 , the characteristic of Comparative Example 14 is indicated by the curve Ln 12 , the characteristic of Comparative Example 15 is indicated by the curve Ln 13 , and the characteristic of Comparative Example 16 is indicated by the curve Ln 14 . 
     The following fact was revealed from the results shown in  FIGS. 13 to 16 . At first, because Co 3 O 4  is not added in Comparative Example 14 (curve Ln 12 ), as shown in  FIG. 13 , Q is too small in the passband (FM band) of the filter for practical use. 
     In Comparative Example 15 (curve Ln 13 ), Co 3 O 4  is added by 0.3 mol %. As shown in  FIG. 13 , the frequency characteristic is improved as compared with Comparative Example 14 (curve Ln 12 ). However, Q is at the peak in the vicinity of 75 MHz, and the curve is sharply lowered when it passes the peak, as being disqualified for the practical use. As shown in  FIG. 14 , the value of the inductance is substantially constant in Example 24 and Comparative Examples 14 and 15. 
     In Comparative Example 16 (curve Ln 14 ) Co 3 O 4  is added by 1.5 mol %. As shown in  FIG. 15 , Q is improved in the passband (FM band) of the filter. However, as shown in  FIG. 16 , the value of the inductance is extremely small. 
     In Example 24 (curve Ln 11 ), ZnO is added by 4 mol %, and Co 3 O 4  is added by 1.5 mol %. According to  FIGS. 13 and 14 , Q and the inductance are improved in the passband (FM band) of the filter. 
     The magnetic material is preferably the Ni—Zn based ferrite having the crystalline structure of the spinel type as described above. However, it is also possible to use hexagonal Ferrox planar ferrite. 
     Next, an explanation will be made below about an example of the method for producing the filter  10 B according to the second embodiment. At first, a green sheet of the dielectric material and a green sheet of the magnetic material were manufactured respectively. 
     The green sheet of the dielectric material was manufactured as follows. That is, respective powders of high purity barium carbonate, strontium carbonate, neodymium oxide, and titanium oxide were weighed in accordance with the respective composition ratios of Examples 1 to 13 shown in  FIG. 10 . The raw material powders were introduced together with a zirconia ball into a pot made of alumina, and subjected to wet blending with ethanol as a dispersion medium. The obtained mixture was taken out from the pot, dried and calcined at 1,200° C. for 2 hours in an air atmosphere. The calcined product was introduced together with an alumina ball into a pot made of alumina, and coarsely pulverized. After that, B 2 O 3 —SiO 2  based glass was added by 3% by weight, followed by being finely pulverized and dried to obtain a powder having an average particle size of about 0.3 μm. A known binder, a plasticizer, and a solvent were mixed with the powder to prepare a slurry. After adjusting the viscosity, the green sheet having a thickness of 0.05 mm was prepared by the doctor blade method. 
     On the other hand, the green sheet of the magnetic material was manufactured as follows. That is, predetermined amounts of respective raw materials of iron oxide (Fe 2 O 3 ), nickel oxide, copper oxide, zinc oxide, and cobalt oxide were weighed, and they were introduced together with a zirconia ball into a pot made of alumina, and subjected to wet blending with ethanol as a dispersion medium. The obtained mixture was taken out from the pot, dried and calcined at 900° C. for 2 hours in an air atmosphere. The calcined product was introduced together with an alumina ball into a pot made of alumina, and coarsely pulverized. After that, the product was finely pulverized and dried to obtain a powder having an average particle size of about 0.5 μm. A known binder, a plasticizer, and a solvent were mixed with the powder to prepare a slurry. After adjusting the viscosity, the green sheet having a thickness of 0.05 mm was prepared by the doctor blade method. 
     After that, each of the green sheet of the dielectric material and the green sheet of the magnetic material was punched into 100×100 mm, and via-holes were formed with a laser. Subsequently, a conductor paste containing a main component of Ag was used to form a predetermined circuit pattern by the screen printing. The green sheets of the dielectric material and the green sheets of the magnetic material were stacked to provide a predetermined arrangement, pressed at a temperature of 80° C. and a pressure of 20 MPa. The laminate was cut, and then a conductor was printed on the end surface, sintered so that the maximum temperature was 900° C. for 2 hours in the air to obtain the product (filter  10 B according to the second embodiment). 
     The filter  10 B according to the second embodiment constructed with the composition as described above was compared with a filter (conventional example) constructed with a base member of a dielectric material in relation to the characteristics (attenuation characteristic and insertion loss characteristic). Results were obtained as shown in  FIGS. 17 to 19 . In  FIGS. 17 to 19 , the solid line Ln 20  indicates the characteristics of the filter  10 B according to the second embodiment, and the broken line Ln 21  indicates the characteristics of the conventional example. 
     As shown in  FIG. 17 , in the conventional example, the deterioration (see, for example, rebounds P 1 , P 2 ) is observed in the attenuation characteristic on the side of the high frequency region (for example, not less than 0.5 GHz). On the contrary, in the case of the filter  10 B according to the second embodiment, no deterioration is observed in the attenuation characteristic on the side of the high frequency region. In relation thereto,  FIG. 18  shows the measurement result up to 6 GHz. From  FIG. 18 , no deterioration is observed in the attenuation characteristic on the side of the high frequency region. 
     As appreciated from  FIG. 19  as well, the insertion loss of the filter  10 B according to the second embodiment is smaller than that of the conventional example. 
     As described above, when the filter  10 B according to the second embodiment is used, for example, it is possible to carry an FM radio receiver and/or an FM transmitter on a portable device. 
     It is possible to further improve the characteristics by combining the filter  10 A according to the first embodiment and the filter  10 B according to the second embodiment. 
     Next, a filter  10 C according to a third embodiment will be explained with reference to  FIGS. 20 to 24 . 
     In the filter  10 C according to the third embodiment, among the dielectric portion  18 , the magnetic portion  20 , and the joint portion  22  shown in  FIG. 2 , the material of the magnetic portion  20  is specified and those of the dielectric portion  18  and the joint portion  22  are the same as or equivalent to that of the filter  10 B according to the second embodiment described above. 
     The magnetic material, which constitutes the magnetic portion  20  of the filter  10 C according to the third embodiment, is preferably ferrite containing a main component of a composition in which NiO is 37.4 to 42.2 mol %, ZnO is 0.01 to 3.6 mol %, Fe 2 O 3  is 46.2 to 48 mol %, Co 3 O 4  is 0.1 to 0.8 mol %, and CuO is 10 to 14 mol %. 
     More preferably, the magnetic material is ferrite containing a main component of a composition in which NiO is 37.4 to 42.2 mol %, ZnO is 0.01 to 1.9 mol %, Fe 2 O 3  is 46.6 to 48 mol %, Co 3 O 4  is 0.1 to 0.5 mol %, and CuO is 10 to 14 mol %. 
     The reason thereof will be explained on the basis of results of a fifth experimental example shown in  FIGS. 20 to 23 . 
     In the fifth experimental example, the temperature coefficient τμ and the high frequency characteristic (frequency for Q=100) are measured when the base member  16  is manufactured with different amounts of Co 3 O 4 , ZnO, Fe 2 O 3 , and NiO added respectively. In  FIGS. 20 to 23 , the solid line Ln 101  indicates the characteristic of the temperature coefficient, and the broken line Ln 102  indicates the high frequency characteristic. 
     In order that the filter characteristic taking the temperature coefficient into consideration is practical, it is necessary that the temperature coefficient τμ is not more than 1,000 ppm/° C., and the high frequency characteristic (frequency for Q=100) is not less than 100 MHz. The first range T 1 , which satisfies this condition (Condition 1), is shown in  FIGS. 20 to 23 . More preferably, the temperature coefficient τμ is not more than 500 ppm/° C., and the high frequency characteristic is not less than 100 MHz. The second range T 2 , which satisfies this condition (Condition 2), is also shown in  FIGS. 20 to 23 . 
     At first, as for Co 3 O 4 , as shown in  FIG. 20 , the temperature coefficient is increased as the amount of addition is increased. This phenomenon may be caused by the high magnetic anisotropy of Co. Such a tendency is also observed that the high frequency characteristic is also increased as the amount of Co 3 O 4  added is increased. It is understood that the high frequency characteristic is slightly lower than 100 MHz when the amount of addition is 0 mol %. 
     Next, as for ZnO, as shown in  FIG. 21 , the temperature coefficient is increased, and the high frequency characteristic is lowered, as the amount of addition is increased. The temperature coefficient exceeds 1,000 ppm/° C. at the stage at which the amount of addition exceeds 3.6 mol %. The high frequency characteristic is 100 MHz at the stage at which the amount of addition is not less than 6 mol %. Therefore, the first range T 1  is determined by the temperature coefficient. 
     As for Fe 2 O 3 , as shown in  FIG. 22 , the temperature coefficient is high and the temperature characteristic is deteriorated outside the first range T 1 . The high frequency characteristic is lowered as the amount of addition is increased. The high frequency characteristic is less than 100 MHz at the stage at which the amount of addition exceeds 48 mol %. 
     As for NiO, as shown in  FIG. 23 , the temperature coefficient is high and the temperature characteristic is deteriorated outside the first range T 1 . However, the high frequency characteristic of not less than 100 MHz can be realized within the measurement range (35 to 49 mol %). 
     The composition range of the magnetic material for forming the magnetic portion  20  described above can be determined from the first range T 1  and the second range T 2  shown in  FIGS. 20 to 23 . 
       FIG. 24  shows results of an experimental example (sixth experimental example) in which the initial magnetic permeability (initial magnetic permeability at a frequency of 10 MHz and a temperature of 25° C.), the temperature coefficient (temperature coefficient at a frequency of 10 MHz), and the high frequency characteristic (frequency for Q=100) are measured for Examples 101 to 108 and for Comparative Examples 101 to 107. In Examples 101 to 108 and Comparative Examples 101 to 107, the amount of addition of CuO is constant (12 mol %) and the amounts of addition of NiO, ZnO, Fe 2 O 3 , and Co 3 O 4  are within the first range T 1  or the second range T 2  described above. In Comparative Examples 101 to 107, CuO added is constant (12 mol %) and the amounts of addition of NiO, ZnO, Fe 2 O 3 , and Co 3 O 4  are outside the first range T 1  described above. 
     According to the results shown in  FIG. 24 , in Comparative Example 101, the temperature coefficient was 860 ppm/° C. which was satisfactory. However, the high frequency characteristic was 70 MHz which was not less than 100 MHz for the practical level. Similarly, also in Comparative Example 106, the temperature coefficient was 360 ppm/° C. which was satisfactory. However, the high frequency characteristic was 65 MHz which was not at the practical level. 
     In any one of Comparative Examples 102 to 105, the high frequency characteristic was not less than 100 MHz of the practical level. However, the temperature coefficient did not satisfy the practical level of not more than 1,000 ppm/° C. 
     In Comparative Example 107, the temperature coefficient did not satisfy the practical level of 1,000 ppm/° C. Further, the high frequency characteristic also did not satisfy the practical level of not less than 100 MHz. 
     On the other hand, in Examples 101, 102, and 104 to 108, the temperature coefficient satisfied the value of not more than 500 ppm/° C., and the high frequency characteristic also satisfied the value of not less than 100 MHz. The satisfactory results were obtained. 
     In Example 103, the result did not exceed the results of Examples 101, 102, and 104 to 108. However, the temperature coefficient satisfied the value of not more than 1,000 ppm/° C., and the high frequency characteristic also satisfied the value of not less than 100 MHz. The satisfactory results were obtained. 
     As described above, both of the temperature characteristic and the high frequency characteristic are satisfactory in the filter  10 C according to the third embodiment. When the filter  10 C is used, it is possible to carry an FM radio receiver and/or an FM transmitter on a portable device, for example. 
     It is possible to further improve the characteristics by combining the filter  10 A according to the first embodiment and the filter  10 C according to the third embodiment. 
     It is a matter of course that the electronic part according to the present invention is not limited to the embodiments described above, which may be embodied in other various forms without deviating from the gist or essential characteristics of the present invention.