LC circuit incorporated ceramic substrate

Abstract: There is provided a monolithic structure of an LC circuit incorporated component comprising at least one capacitor formed from internal electrodes in layered form in a ceramic monolithic structure, at least one inductor formed from internal conductive structure in coil form in said monolithic structure, internal connecting leads for connenting said capacitor(s) and inductor(s) to form said circuit, formed in said structure, and terminals for the circuit, formed at the surface(s) of the component.

Description: Field of the Invention The present invention relates to a monolithic structure of an LC circuit comprising a plurality of layers of a sintered ceramic composite material. Particularly, it relates to a monolithic structure of an LC circuit comprising a plurality of layers of a sintered ceramic composite material including both capacitance and inductance circuits. Description of the Prior Art Many attempts have been made to provide miniaturization of integrated circuits in the same ceramic material incorporating both capacitance function and inductance function. However, there have not been found ceramic materials having both features of dielectricity to provide capacitance function and of magneticity to provide inductance function. There have been many attempts of miniaturization of an integrated circuit substrate incorporating both of capacitance function and inductance function. However, there have been provided no materials having dielectricity enough to provide capacitance and magneticity enough to provide inductance, and then, the conventional LC incorporated ceramic component has been produced by firing separately a multilayered capacitance element and a multilayered ceramic inductance element, and then combining or adhering the two fired elements. The alternative method of production of such conventional LC incorporated component comprises forming separately a ceramic green shaped body having capacitance electrodes and a ceramic green body having inductance feature. Because such method uses at least two different species of materials, the production process is complicated and further, the levels of the top surface of the dielectric layered body and the magnetic layered body should be at the same level. There are known ceramic multilayered structures incorporating capacitors, as disclosed in U.S. Patent No.4,082,906, in which monolithic capacitors are fired with incorporating internal electrodes in a dielectric ceramic body, and further outer electrodes therefor. USP No. 4,322,698 discloses an LC-composite component comprising capacitor and inductor layers made of different materials. USP No. 4,573,101 suggests an LC-composite structure, wherein an inductor is formed on a capacitor, the layers forming the inductor and the capacitor are made of different materials. USP No. 4,689,494 discloses an inductor consisting of a multi-layer chip coil comprising a stack of intermediate laminas of magnetizable material having a through-hole defined therein. Summary of the Invention With the foregoing considerations in mind, the present invention contemplates the provision of a ceramic multilayered discrete component incorporating capacitance and inductance circuits. It is an object of the present invention to provide a new structure of an LC circuit incorporated discrete component in form of a monolithic multilayered ceramic structure (monolithic structure of a LC circuit comprising a plurality of layers of a sintered ceramic composite material). It is another object of the present invention to provide a discrete LC incorporated component which can be economically fabricated and and has significantly improved electric properties. These objects are solved by a monolithic structure of an LC circuit comprising a plurality of layers of a sintered ceramic composite material according to claim 1. As described in the foregoings, the inventive discrete component incorporating capacitance and inductance circuit will enable economical process for manufacturing a monolithic circuit component having LC circuit. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an exploded view of the inventive structure of a ceramic substrate incorporating LC circuit, wherein each conductive pattern incorporating layer to be stacked into the inventive structure is shown respectively and separately, and a top insulating layer and glass layer to be stacked on the top of the structure are shown as a and a'. FIG. 2 illustrates an equivalent circuit diagram formed in the structure shown in FIG. 1. FIG. 3 shows a sectional view of the structure shown in FIG. 1. FIGS. 4 A, B, C, D, E and F are graphs showing the dependence of the dielectric constants and magnetic permeability of the composition, on the ceramic component ratio of barium titanate and ferrite. Detailed Description of Preferred Embodiments The composite material for the monolithic body of the invention is a combination of ferrite of the formula: MFe₂O₄, wherein M is one or more in combination, selected from the group consisting of manganese, nickel, magnesium, cobalt, copper, zinc and iron, and of a dielectric material of one or more in combination selected from the group consisting of barium titanate BaTiO₃, lead titanate PbTiO₃ and strontium titanate SrTiO₃. This sintered body is used to compose the substrate or the material for multilayered circuit having the inventive structure. This composite sintered body has both of magnetic permeability and dielectric constant, both of which can be appropriately selected or chosen. The fired ceramic material for use in such a sintered body has preferably a dielectric constant of higher than 20, and a permeability of more than one. When the dielectric constant is less than 20, the capacity formed in the layered component will be not enough. On the other hand, when the permeability is less than one, the magneticity is not enough to form an inductance in the layered body. In accordance with the inventive monolithic structure of the LC-incorporated ceramic multilayered component, internal electrodes for the capacitance and an internal conductive structure in coil form for the inductance circuit are formed in the ceramic composite multilayered structure having both of high dielectricity and magneticity integrated therein. The ceramic composite structure is produced by mixing powder of titanate dielectric material having size of 30 to 120 microns and powder of ferrite magnetic material having the similar size, and forming a slurry from the mixture, and forming thin ceramic films from the slurry, and firing the films, and stacking the fired films with internal conductive coil structure(s) and internal electrodes therein in a predetermined geometry and configuration, so as to form a stacked body of the ceramic structure containing these internal conductive coil structure and internal electrodes, and further firing the resulting stacked body to produce the LC incorporated monolithic component. The starting material powders have a grain size of 30 to 120 microns. When the size is less than 30 microns, the materials of ferrite and dielectric composition would be reacted together in the firing process, to produce undesired compounds having not enough dielectricity and magneticity. Further, when the size of the starting materials is higher than 120 microns, a local distribution, or localization of dielectricity and permeability is generated within the structure of the component, so as to provide instability in capacitance and inductance formed in the structure. The new composite structure of the present invention uses at least one dielectric compound selected from barium titanate BaTiO₃, lead titanate PbTiO₃ and strontium titanate SrTiO₃, or combinations thereof, and for instance a Ni-Zn ferrite compound composition. Within the composite multilayered structure, internal conductive layers are formed in a predetermined geometry and configuration using a conductive paste of metal(s) selected from gold (Au), silver (Ag), copper (Cu) and palladium (Pd). The green films formed from the new composition having a desired dielectric constant and permeability are stacked with forming predetermined patterns on and in the green films being stacked, and then the stacked body with the internal conductive structure and internal electrodes is fired to produce the monolithic component incorporating LC-circuits. The material for the internal electrodes to make a capacitor in the new structure or new geometry in the monolithic component is preferably highly conductive, heat-resistant, weather-resistant (durable) composition usable to form a thin film, which is preferably consisting essentially of Ag. The internal electrodes can be formed by using a conventional printing lithography. Further, the internal conductive structure to make an inductance circuit in the new structure of the monolithic component is preferably highly conductive, and can be the same material for the above-mentioned internal electrodes. The terminals for such capacitor(s) and inductor(s) circuit are formed at the outer surface(s) of the ceramic structure by forming conductive paste patterns connecting the capacitor or inductor on the surface or edge of the ceramic structure, and firing the paste patterns together the stacked ceramic structure. Alternatively, the terminals can be on or in the edge(s) of the structure in various forms to form conductive thin film(s) used as an electrode. The new structure having both of capacitor(s) and inductor(s) circuit(s) can be fabricated by any of multilayering techniques. For example, ceramic sheets of the above-mentioned composition are formed, and then, conductive paste is applied on the surfaces of the formed sheets to form pattern for internal electrodes and internal conductive coil structure, and the sheets with such patterns are stacked to a stacked ceramic body, which body is fired. Alternatively, a multilayered structure with internal electrodes and internal conductive coil configuration is formed by using paste of the above-mentioned dielectric and magnetic composition, and a conductive paste applied by a printing technique, and the multilayered structure is fired to form a ceramic fired body with internal electrodes to form capacitor(s) and internal conductive coil structure to form inductor(s) therein. FIG. 1 illustrates schematically the inventive monolithic structure of the LC circuit incorporated component, wherein ceramic insulating film (a) covers a composite ceramic structure having a composite ceramic composition formed from ferrite material and dielectric material powders, with conjunction layer (a') of glass. Outer terminals such as A₀, B₀, C₀ and D₀ are formed at the surface of the cover film a, and leads formed in a throughhole in the films (a) and and in a conjunction layer ( glass layer ) (a') connect the inner terminals A₁, B₁, C₁, and D₁ of a capacitor formed in the ceramic structure to the terminals such as A₀. Internal electrodes C₅ and D₇ formed in the ceramic structure will construct a capacitor, and on the other hand the internal conductive structure A₁ to A₁₅ and B₁ to B₁₅ formed in coil form in the ceramic structure will construct an inductor. Then, each of the internal electrodes and the internal conductive structure has outer terminals such as A₀, B₀, C₀ and D₀. Further, leads or connecting patterns can be formed in a conjunction layer (a) on the surface of the structure, in a predetermined circuit pattern, or a predetermined geometry. Preferably, the firing temperature should be high enough to result in sintering of the body, but not so high to cause chemical reaction between the dielectric compound(s) and magnetic compound(s). The present invention is further illustrated by the following example to show manufacture of the inventive ceramic structure incorporating LC circuit, using Ni-Zn ferrite (Ni 0.3 Zn 0.7 )Fe₂O₄ and barium titanate BaTiO₃, but should not be interpreted for the limitation of the invention. EXAMPLE [ Preparation of Starting Particulate Materials ] Powders of NiCO₃, ZnO and Fe₂O₃ were used as starting materials, in a molar ratio of NiO:ZnO:Fe₂O₃ = 3:7:10, and ground together, and were calcined at 1,000 °C, and milled to provide powder of (Ni 0.3 Zn 0.7 ) Fe₂O₄. On the other hand, BaCO₃ and TiO₂ powder were used as starting materials in a molar ratio of BaCO₃:TiO₂ = 1:1, and ground and fired at about 1,150 °C, and then milled to provide powder of BaTiO₃. Next, the powders of (Ni 0.3 Zn 0.7 )Fe₂O₄ and BaTiO₃ were mixed in a predetermined ratio, and organic binder was added to the mixture to produce a powder paste of dielectric material and magnetic material. A conductive paste of Pd (or Ag/Pd) was used to form conductive patterns for the inventive structure. The conductive patterns can be formed in the structure in form of layers for the formation of capacitance and inductance. The resulting green body of the structure was fired at the temperature of about 1250 °C for four to ten hours resulting in the multilayered LC-incorporated component. [ Structure of Green Stacked Body for the LC-circuit Incorporated Component ] The fired films as shown in FIG. 1 were stacked with insertion of conductive layers of the predetermined patterns to form patterns for coil-shaped conductive structure and multilayered capacitors in the ceramic layered structure as shown in FIG. 1, together with the terminals such as A₀, B₀, C₀ and D₀ at the surface of the component. Further, throughholes were formed in the layered composite to produce the terminals for capacitors and inductance elements, at the surface of the ceramic layered structure. Next, finally glass paste was applied on the surfaces of such structure, excepting on the surfaces of the terminals for the capacitor(s) and the inductance element(s) by using a printing technique. Further, alumina film having 100 microns with glass coating as to face to the glass paste coating was applied to the surface of the structure, and the pressure was applied on the composite structure, and then, the composite structure was heated with pressure at the temperature of 500 °C to 800 °C so as to form adhesion of the alumina film to the surface of the ceramic structure. The resulting composite structure has LC circuit therein. FIG. 1 shows an exploded view of the whole component incorporating LC circuit, wherein FIG. 3 shows a sectional view of the inventive structure of FIG. 1. FIG. 2 shows an equivalent circuit formed in the structure shown in FIG. 1. The LC-incorporated discrete component of FIG. 1 has a ceramic multilayered structure of dielectric and magnetic composite material, internal facing electrodes C₅ and D₇ formed of Ag/Pd conductive paste to form the capacitor, and internal electrode as A₁ to A₁₅ and B₁ to B₁₅ in FIG. 1, formed of the same paste to form the inductor, as shown in FIGS. 1 and 3. The internal structure within the ceramic composite multilayered body is in section, as shown in FIG. 3. The left portion of the ceramic structure of FIG. 1 contains internal electrodes C₅ and D₇ facing together to form a capacitor. Then, each of inner terminals C₁ and D₁ formed on the surface of the body is connecting respectively to the outer terminals C₀ and D₀. The right portion of the ceramic structure of FIG. 1 contains an inductor structure A₁ to A₁₅ and B₁ to B₁₅, that is, an internal conductive structure in coil form so as to form an inductor. Therefore, the inventive discrete component has both of capacitors and inductor in the ceramic composite body. In accordance with the present invention, the composite materials to form the ceramic structure are formed from the combination of various ferrite materials and dielectric materials. Then, for comparison, FIGS. 4 A, B, C, D, E and F show the relation of the composition to the dielectric constant and permeability of the resulting composite materials. The graphs of FIGS. 4 A to F show the result of the measurement of dielectric constant and permeability in regard to the composite ceramic materials prepared from the predetermined combination of BaTiO₃ powder having grain size of 50 to 100 microns, and ferrite material having grain size of less than 10 microns. BaTiO₃ powder having grain size of 50 to 100 microns, and ferrite material having grain size of less than 10 microns were mixed in a predetermined ratio, and molded into a disc shape. The disc was heated to the temperature of 1,250 °C at a raising rate of 400 °C/hour and maintained at the temperature of 1,250 °C for four hours and naturally cooled. The fired sample disc was measured on dielectric constant and permeability in accordance with a standard method by using LCR meter (YHP 4278A) available from Yokokawa Hewlett Packard. Within the ceramic body of the above-mentioned composite material, the internal electrodes, i.e. internal conductive patterns C₁ to C₅ and D₁ to D₇ to form a capacitor, and connecting to the outer electrodes(terminals) C₀ and D₀ are formed to the capacitor C of FIG. 2, and further, the internal conductive structures, i.e. conductive patterns A₁ to A₁₅ and B₁ to B₁₅, in coil form are formed within the ceramic body, so as to form inductors L₁ and L₂ of FIG. 2. Further, the outer terminals A₀, B₀, and C₀ are on the surface of the outer insulating sheet adhered on the LC-incorporated discrete component (a) by a printing technique so as to form the desired circuit or patterns. Further, on the outer surface(s) of the inventive LC-incorporated discrete component, the outer electrodes A₀, B₀, and D₀ are formed by a printing lithography to produce the desired circuit(s), and further, a tip element such as a transistor can be provided on the surface, so as to produce complex circuits, or hybrid circuit. As described in the foregoing, the inventive ceramic structure incorporating LC circuit will enable to miniaturize the integrated circuit including capacitance and inductance circuit(s). Further, the inventive structure can enable to facilitate the LC-incorporated discrete component.

Claims: A monolithic structure of an LC circuit comprising (a) a plurality of layers of a sintered ceramic composite material forming a monolithic body, the ceramic composite material being a mixture of dielectric and magnetic materials fired from starting material powders having a grain size of 30 to 120 micrometers, wherein the dielectric material is selected from barium titanate, lead titanate and strontium titanate or combinations thereof, and said magnetic material is selected from ferrite of the general formula: MFe₂O₄, Wherein M is a metal selected from the group consisting of manganese, nickel, magnesium, cobalt, copper, zinc and iron, or combinations thereof; (b) at least one capacitor formed from internal electrode layers within the monolithic body; (c) at least one inductor formed from internal conductive structures in coil form within said monolithic body; (d) internal connecting leads for connecting said capacitor(s) and inductor(s) to form said LC circuit; and (e) terminals for the LC circuit, formed at the surface(s) of the monolithic body. The structure as claimed in claim 1, wherein at least one of said leads is formed in a throughhole formed in said monolithic body. The structure as claimed in claim 1 or 2, wherein said monolithic body has adhered to at least on one of its surfaces a prefired insulating ceramic film. The structure as claimed in claim 3, wherein said ceramic film is adhered by means of at least one of a solder layer, a glass layer and a thick coating conductive paste layer.

Inventors: KITAHARA NAOTO, KOSHIMURA MASAMI, ONO MIKIYA, KITAHARA, NAOTO, KOSHIMURA, MASAMI, ONO, MIKIYA
Applicants: MITSUBISHI MATERIALS CORP, MITSUBISHI MATERIALS CORPORATION
Application year: 1990
Main classification: H01L27
IPC codes: H01L27, B32B15, H05K1, H03H7, H05K3, C04B37, H01G4