Recent size, and weight reductions of various types of electronic equipment have accelerated to diminish the size, and weight of electronic parts of which they are made up. This is also true of coils, transformers or the like, and so their size, and weight are now reduced. To reduce the size, and weight of electronic equipment on the one hand, and to enable the equipment to be used at higher frequencies on the other hand, coils or other inductance elements are designed to be used at higher frequencies. In drastically popularized mobile communication fields in particular, coils are now used at a frequency band of 100 MHz or higher.
Magnetic materials, and non-magnetic materials are available for inductance elements, and spinel ferrites are used for the magnetic materials while dielectric ceramics such as alumina, and glasses are used for the non-magnetic materials. In particular, the spinel ferrites have permeability due to their cubic crystal structure, and so are advantageous over air-core coils or inductance elements built up of non-magnetic materials because the number of turns can be decreased with an increased inductance. For this reason, various inductance elements inclusive of coils, and transformers, for the most part, are made up of spinel ferrites.
However, the permeability of spinel ferrites has close relations to frequency, and has a characteristic feature of decreasing sharply from a certain frequency. Thus, their inductance, too, drops at a band exceeding that frequency. Here note that the relation "Snoek's limit line" exists between the permeability of ferrites and frequency. In other words, if a ferrite of low permeability is used to extend permeability to a high frequency region, it can then be used as an inductor for high frequency purposes. Ni-based spinel ferrite material having relatively low permeability is used for such an inductor for high frequency purposes. To make an inductor element for high frequency purposes in particular, Ni-based spinel ferrite material having a permeability as low as about 1 to 3 is used, as set forth in JP-B-7-24242. In this case, a ferrite with its Curie point lower than a practically usable temperature is typically used as material having a permeability of 1.
A spinel ferrite, because of being a solid solution of Fe.sub.2 O.sub.3 and an oxide with a divalent metal ion, is produced by mixing Fe.sub.2 O.sub.3 powders with powders of the oxide with a divalent metal ion, and firing the mixture. As the divalent metal ion for Ni systems, Cu, Zn, etc. are used in addition to Ni. However, oxides of Ni, Cu, etc. are expensive, ending up with an increase in the cost of ferrite. A particularly grave problem with such ferrite is that its high frequency characteristics are insufficient, and its Q value is low at 200 MHz or higher as well.
Besides ferrites, alumina, glasses, and resins are primarily available as materials for high frequency inductance elements. However, these materials offer the following problems.
Alumina or a substance having the chemical formula Al.sub.2 O.sub.3 excels in various properties such as heat resistance, resistance to thermal shock, chemical resistance, wear resistance, electrical insulating properties, hardness, and mechanical strength, and so find applications in wide fields inclusive of substrates, grinding chips, crucibles, and building materials, to say nothing of inductance elements. This alumina has also the properties required for core materials for coils used even in a high frequency region, i.e., low permeability and high electrical resistance. For this reason, the alumina is employed as core material used in a high frequency region, as set forth in JU-A-5-7211. However, the temperature at which pure (high-purity) raw material powders are sintered is very high (about 1,800.degree. C.), posing a problem in connection with the durability of equipment, etc. Consider here that sintering is carried out at 1,200.degree. C. or higher with the addition of SiO.sub.2, CaO, MgO, etc. Then, an additional step of blending these components is needed. Furthermore, the high hardness of alumina poses some problems; for instance, it wears away the production equipment used for such blending, e.g., media, and gives rise to contamination due to debris resulting from the wear of such media, and equipment. This wear problem also holds for other equipment, for instance, molds and punches in molding equipment, and causes the overall durability of a production system to become worse. Especially when cores for inductance elements are produced, molds, etc. are likely to wear away, producing an adverse influence on core products, and so posing a grave production problem. This is because it is preferable for such cores to have collars at both their ends, or take E, F, and irregular forms, rather than simple cylindrical, and columnar forms. In a mass-production system, on the other hand, wire materials are automatically wound on cores. In particular, recent electronic parts are increasingly provided in the form of surface mount devices (SMDs), and are often packaged by means of an automated packaging machine. When an automated winding machine is used to wind a wire material on a core for coil production, however, not only does a portion of contact of a core-fixing jig with the core wear away, but also a portion of contact of the wire material with the core wears away during winding, resulting in defects such as winding failure, short-circuiting, and disconnection. In the automated packaging machine, too, a portion of contact of its chuck (handling area) with cores wears away during part packaging, again posing a similar problem.
A glass is a non-crystalline substance, and refers generally to a silicate glass comprising SiO.sub.2 and a metal oxide. Glasses, because of excelling in optical properties, are utilized for not only inductance elements but also window glasses, optical fibers, optical lenses, etc. Typical of glasses used for inductance elements is a borosilicate glass comprising boron oxide (B.sub.2 O.sub.5) and silicon oxide (SiO.sub.2), and obtained by melting a mixture of B.sub.2 O.sub.5, SiO.sub.2 and the like. However, these glasses have fragile mechanical strength in themselves. For this reason, they fail during chucking or the like by an automated packaging machine, and so are practically disabled, resulting in low product yields.
A resin is a substance comprising complicated organic acids, and their derivatives, and now find applications in wide fields. The resin has a characteristic feature of melting, and burning at relatively low temperatures, and so being poor in heat resistance. A problem with using the resin as an element is that difficulty is involved in the direct soldering of the resin onto a substrate. Another problem is that the resin is weaker in mechanical strength than ceramics.
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