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Dokumentenidentifikation EP1050889 15.03.2007
EP-Veröffentlichungsnummer 0001050889
Titel Magnetischer Ferrit-Film und Herstellungsverfahen
Anmelder Kawatetsu Mining Co., Ltd., Tokio/Tokyo, JP
Erfinder Fukuda, c/o Kawasaki Steel Corporation, Yasutaka, Tokyo 100-0011, JP;
Tachi, c/o Kawatetsu Mining Co., Yoshihito, Tokyo 111-0051, JP
Vertreter derzeit kein Vertreter bestellt
DE-Aktenzeichen 60033082
Vertragsstaaten DE, FR, GB, NL
Sprache des Dokument EN
EP-Anmeldetag 19.04.2000
EP-Aktenzeichen 003033412
EP-Offenlegungsdatum 08.11.2000
EP date of grant 24.01.2007
Veröffentlichungstag im Patentblatt 15.03.2007
IPC-Hauptklasse H01F 1/00(2006.01)A, F, I, 20051017, B, H, EP
IPC-Nebenklasse H01F 41/16(2006.01)A, L, I, 20051017, B, H, EP   

Beschreibung[en]

The present invention relates to a magnetic ferrite film for magnetic devices, in particular, to one with improved adhesiveness to Si substrates, and to a method of producing the same.

Small-sized and lightweight portable appliances capable of being driven by battery power are in great demand. It is desirable that applications for multi-media information services, have advanced functions including communication and display functions, and also have the capabilities of rapidly processing large-scale information media including images, etc. With these, there is an increasing demand for power sources capable of converting a single voltage from batteries to a plurality of different voltages applicable to different types of devices such as CPUs, LCD modules, power amplifiers for communication, etc. For small-sized and lightweight portable appliances with such advanced functions, the important theme is to realize small-sized, high-efficiency power sources.

At present, DC-DC converters are used in which the direct current inputted is intermittently controlled by the action of a semiconductor switch to give a stable, desired voltage output. The Journal of the Applied Magnetics Society of Japan, Vol. 20, No. 5, 1996, p. 922, describes a power source with a plane inductor mounted thereon, in which the inductor comprises a thin magnetic film. Japanese Patent Laid-Open No. 134820/1997, discloses a plane magnetic device (e.g., inductor, etc.) with a plane coil being sandwiched between a soft magnetic substance via an insulator therebetween, in which the plane coil conductor is composed of a plurality of conductor lines divided in different sections. These are suitable for thin devices, and are expected to be used in the field of portable appliances and others that are required to be small-sized and lightweight.

However, the conventional plane inductors are produced by forming a magnetic metal film of from 6 to 7 µm thick on Si substrates through sputtering or the like. Therefore, as compared with those for other conventional inductors with a conductor line wound around a sintered ferrite core, the production costs for such plane inductors inevitably increase, which is a bar to industrialization of the plane inductors. To solve this problem, the present inventors have already proposed a technique of substituting the magnetic metal film in those plane inductors with a magnetic ferrite film to be formed through printing or the like (see Japanese Patent Laid-Open No. 11-26239/1999).

However, the technique requires further improving the adhesiveness of the magnetic ferrite film to Si substrates. If its adhesiveness thereto is not good, the magnetic ferrite film will peel away from Si substrates in the process of fabricating magnetic devices comprising the film-coated substrate, and the reliability of the devices fabricated will be thereby lowered.

Thus, it is desirable to increase the adhesiveness of a magnetic ferrite film to Si substrates thereby to improve the reliability of thin-film magnetic devices comprising the film-coated substrate.

JP-A-11 026239 by the present applicant discloses a magnetic ferrite film and a method of forming the same according to the preamble of each of claims 1 and 11, in which the film has a CuO content of 4%. Other films are disclosed by this document as having a CuO content throughout the film greater than 5%.

JP-A-08 288139 by Kyoshiro Seki discloses a magnetic ferrite film which is free of CuO.

According to a first aspect of the invention there is provided a magnetic ferrite film formed on a Si substrate for magnetic devices, wherein the magnetic ferrite film contains CuO and is formed on the surface of the Si substrate through printing and sintering characterised in that

the CuO content in the film directly adjacent to the surface of the Si substrate is at most 5 mol% whereas the CuO content in the other parts of the film is greater than 5 mol% to at most 20 mol%.

According to a second aspect of the present invention there is provided a method of forming a magnetic ferrite film on a silicon substrate as defined above, comprising the steps of:

  1. a) applying a first ferrite layer, having a CuO content of not larger than 5 mol%, onto the substrate; and
  2. b) applying over said first ferrite layer at least one other ferrite layer having a CuO content larger than 5 mol% and up to 20 mol%.

Preferred embodiments of the invention will now be described by way of example.

The inventors have discovered that the CuO content of part of a magnetic film directly adjacent to a Si substrate should be at most 5 mol%. The reason is as follows: The present inventors have assiduously studied the adhesiveness of magnetic ferrite films to Si substrates and have found that a Cu-Si rich deposit phase, when formed in an interface between the magnetic film and the Si substrate through the reaction of Cu in the magnetic film with Si of the substrate, significantly lowers the adhesiveness between the magnetic film and the Si substrate. On the basis of this finding, it has been concluded that reducing the Cu-Si rich deposit phase in the interface between the magnetic film and the Si substrate results in the increase in the adhesiveness therebetween. For this, the CuO content of the magnetic ferrite film at least in the part of the film existing around the interface between the film and the Si substrate should be at most 5 mol%. If it is larger than 5 mol%, the Cu-Si rich deposit phase will be much formed around the interface between the magnetic film and the Si substrate, thereby lowering the adhesiveness therebetween. Therefore, in the invention, the CuO content of the magnetic ferrite film around the interface between the film and the Si substrate is defined to be at most 5 mol% For this, the CuO content of the magnetic ferrite film, is defined to be at most 5 mol% only in the area around the interface between the film and the Si substrate, while in the other areas the CuO content is over 5 mol%.

To produce a magnetic ferrite film of that type, for example, a first ferrite layer having a CuO content of not larger than 5 mol% is printed on an Si substrate, and the second and other ferrite layers having a CuO content of larger than 5 mol% are printed over the first layer. In this process, the thickness of the first layer (having a CuO content of not larger than 5 mol%) varies, depending on the printing condition employed, but may be generally at most about 1 µm or so. In practice, therefore, a ferrite layer having a CuO content of at most 5 mol% shall be realized within the range of up to about 1 µm from the interface between the layer and the Si substrate.

So far as the CuO content of the magnetic ferrite film is not larger than 5 mol % in the interface between the film and the Si substrate, good adhesiveness of the film to the substrate can be ensured. In this case, preferably, the magnetic film is of a spinel ferrite comprising from 40 to 50 mol% of Fe2O3, from 15 to 35 mol% of ZnO, up to 20 mol% of CuO, and from 0 to 10 mol% of Bi2O3 with NiO and inevitable impurities as the balance, for the average composition of the entire film. The reason why the composition of the magnetic film is defined as above is mentioned bellow.

Fe2O3, from 40 to 50 mol%:

If Fe2O3 is over 50 mol%, Fe2+ ions existing in the film will greatly lower the electric resistance of the film. The reduction in the electric resistance of the film shall increase the ferrite core loss. On the other hand, if Fe2O3 is below 40 mol%, the inductance of the film will be greatly lowered. Therefore, Fe2O3 is defined to fall between 40 and 50 mol%.

ZnO, from 15 to 35 mol%:

ZnO has great influences on the inductance and the Curie temperature of the film. Preferably, the Curie temperature of the film is not lower than about 120°C. If ZnO is below 15 mol%, the inductance of the film will be lowered even though the Curie temperature thereof could be high. On the other hand, if ZnO is above 35 mol%, the Curie temperature of the film will be low even though the inductance thereof could be high. Therefore, ZnO is defined to fall between 15 and 35 mol%.

CuO, up to 20 mol%:

CuO is added to the film so as to lower the temperature at which the film is sintered. The CuO content of the film is defined to be at most 5 mol% in the area around the interface between the film and the underlying Si substrate, as so mentioned hereinabove. In the other area, if CuO is above 20 mol%, it could lower the sintering temperature but will reduce the inductance of the film. Therefore, the uppermost limit of CuO is defined to be 20 mol%.

Bi2O3, from 0 to 10 mol%:

Like CuO, Bi2O3 also acts to lower the sintering temperature. If Bi2O3 is above 10 mol%, it could lower the sintering temperature but will reduce the inductance of the film. Therefore, the uppermost limit of Bi2O3 is defined to be 10 mol%. If the sintering temperature does not need to be lowered, no Bi2O3 need be added to the film.

Actual synthetic products of ferrite generally have a complicated structure comprising plural metal ions of different valences. In the present invention, however, the metal ions constituting ferrite are expressed as their oxides, concretely as Fe2O3, NiO, ZnO and CuO in which Fe is a trivalent ion, and Ni, Zn and Cu are divalent ions.

The method of producing the magnetic ferrite film of the invention is not specifically defined. Preferably, the film is produced by mixing a ferrite powder having been previously prepared to have a predetermined composition, with a binder such as ethyl cellulose or the like to give a paste, then applying the resulting paste onto an Si substrate, and sintering it at a temperature falling between 920 and 1250°C. While the ferrite powder is mixed with a binder, a solvent such as butylcarbinol, terpineol or the like may be added thereto, if desired. Any method of applying the paste onto an Si substrate may be employed, including, for example, screen printing, doctor blade coating, etc. On the surface of the ferrite film thus formed in the manner as above, a plane-structured coil pattern is formed through metal plating or the like; and another magnetic ferrite or metal film is formed over the patterned surface. In that manner, magnetic devices such as transformers, inductors and others comprising the magnetic ferrite film of the invention are fabricated.

The invention is described in more detail with reference to the following Examples, which, however, are not intended to restrict the scope of the invention.

Example 1:

A first ferrite layer to have a thickness of 7 µm (this is after sintered, and the same shall apply hereunder) and a second ferrite layer to have a thickness of 30 µm were formed on an Si substrate by printing, and then sintered in air at a temperature falling between 920 and 1250°C. The CuO content of the second layer was settled to be 15 mol%, while that of the first layer was varied to fall between 0 and 15 mol% as in Table 1 below. 100 samples thus prepared (all having a pattern profile of 5 x 5 mm) were left in an atmosphere at 85°C and 98 % RH (relative humidity) for 4 hours, and then subjected to an adhesive tape peeling test. After the test, the number of samples not peeled were counted. In addition, the peeled interface was observed with a microscope, and the areal ratio of the Si-Cu rich phase thus deposited around the interface was measured. The data obtained are given in Table 1. As in Table 1, it is understood that 75 % or more samples in which the CuO content of the first ferrite layer directly adjacent to the Si substrate is not larger than 5 mol% are good with no peeling of the ferrite layer from the substrate. This supports good adhesiveness of the magnetic ferrite film to the Si substrate in those samples. Referring to the Si-Cu rich phase deposited around the interface between the ferrite film and the Si substrate, the samples in which the areal ratio of the Si-Cu rich deposit phase is at most about 50 % are good, as the adhesiveness between the ferrite film and the Si substrate therein is high. Table 1 No. CuO Content of First Layer (mol%) Adhesiveness (%) Areal Ratio of Si-Cu Rich deposit Phase (%) Case 1 of the Invention 0 99 0 Case 2 of the Invention 1 90 20 Case 3 of the Invention 3 80 30 Case 4 of the Invention 5 75 48 Comparative Case 1 6 40 70 Comparative Case 2 9 30 75 Comparative Case 3 15 20 80

Example 2:

On an Si substrate, formed was a lower magnetic ferrite film through printing and sintering. In these samples prepared herein, the composition of the first layer of the lower magnetic ferrite film for Cases 5 to 15 of the invention was Fe2O3/ZnO/CuO/Bi2O3 = 49/23/0/0 (mol%, with NiO as the balance), and that of the first layer of the lower magnetic ferrite film for Comparative Case 4 was Fe2O3/ZnO/CuO/Bi2O3= 49/23/8/5 (mol%, with NiO as the balance); the thickness of the first layer was 5 µm; the composition of the second layer of the lower magnetic ferrite film was as in Table 2; and the thickness of the second layer was 30 µm. Over the lower magnetic ferrite film thus formed on the Si substrate, a spiral, plane copper coil was formed by plating, and this was covered with an upper magnetic film of amorphous Fe59Co20B14C7 (6 µm). The inductors thus prepared were tested for the inductance at 5 MHz, and their Curie temperature was measured. The data obtained are given in Table 2. In addition, these samples were left in an atmosphere at 85°C and 98 % RH for 4 hours, and then subjected to the same adhesive peeling test as above. After the test, the samples of Cases 5 to 15 of the invention did not peel; but those of Comparative Case 4 peeled. From Table 2, it is understood that the samples of the invention, in which the CuO content of the magnetic ferrite film directly adjacent to the surface of the Si substrate is at most 5 mol% and in which the magnetic ferrite film comprises, on average of the entire film, from 40 to 50 mol% of Fe2O3, from 15 to 35 mol% of ZnO, up to 20 mol% of CuO, and from 0 to 10 mol% of Bi2O3 with NiO as the balance, all have high inductance and high Curie temperature, and are all excellent magnetic devices. Table 2 No. Fe2O3 mol% ZnO mol% CuO mol% Bi2O3 mol% Inductance µH (5 MHz) Curie Temperature (°C) Case 5 of the Invention 49 23 20 0 1.4 330 Case 8 of the Invention 49.5 20 12 0 1.2 320 Case 10 of the Invention 38 30 12 0 0.6 190 Case 11 of the Invention 51 22 12 0 0.4 320 Case 12 of the Invention 49 13 15 2 0.6 390 Case 13 of the Invention 49 37 10 2 1.1 50 Case 14 49 25 22 2 0.5 260 Comparative Case 4 52 20 10 12 0.3 300

According to the invention, a magnetic ferrite film is provided for magnetic devices, whose adhesiveness to Si substrates is much improved. The reliability of the magnetic devices comprising the film of the invention is therefore better than that of conventional magnetic devices.


Anspruch[de]
Magnetischer Ferritfilm, der auf einem Si-Substrat für magnetische Vorrichtungen gebildet wird, wobei der magnetische Ferritfilm CuO enthält und auf der Oberfläche des Si-Substrats durch Drucken und Sintern gebildet wird, dadurch gekennzeichnet, dass der CuO-Gehalt in dem direkt an die Oberfläche des Si-Substrats angrenzenden Film höchstens 5 Mol-% beträgt, wohingegen der CuO-Gehalt in anderen Teilen des Films höher als 5 Mol-% bis höchstens 20 Mol-% beträgt. Magnetischer Ferritfilm nach Anspruch 1, wobei das Flächenverhältnis der Si-Cureichen Phase an der Grenzfläche zwischen dem magnetischen Film und dem Si-Substrat höchstens 50% ist. Magnetischer Ferritfilm nach Anspruch 1 oder Anspruch 2, der gebildet wird, indem eine ferritpulverhaltige Paste auf ein Si-Substrat aufgetragen und dieses in der Folge gesintert wird. Magnetischer Ferritfilm nach einem der Ansprüche 1 bis 3, wobei das Sintern bei einer Temperatur zwischen 920 und 1250°C durchgeführt wird. Magnetischer Ferritfilm nach einem der Ansprüche 1 bis 4, der durchschnittlich auf dem gesamten Film bezogen von 40 bis 50 Mol-% Fe2O3, von 15 bis 35 Mol-% ZnO, bis zu 20 Mol-% CuO und von 0 bis 10 Mol-% Bi2O3 mit NiO und unvermeidbaren Verunreinungen als ausgleichenden Rest umfasst. Magnetische Vorrichtung, umfassend den magnetischen Ferritfilm nach einem der Ansprüche 1 bis 5. Elektrisches Gerät, umfassend die magnetische Vorrichtung aus Anspruch 6. Verfahren zur Bildung eines magnetischen Ferritfilms auf einem Silikonsubstrat, wie nach einem der Ansprüche 1 bis 5 beansprucht, gekennzeichnet durch die Schritte: a) Auftragen einer ersten Ferritschicht mit einem CuO-Gehalt von nicht mehr als 5 Mol-% auf das Substrat; und b) Auftragen von mindestens einer anderen Ferritschicht mit einem CuO-Gehalt von mehr als 5 Mol-% bis zu 20 Mol-% über diese erste Schicht. Verfahren nach Anspruch 8, wobei die Stufe b) das Sintern umfasst, um auf dem Si-Substrat einem magnetischen Ferritfilm mit einer durchschnittlichen Zusammensetzung, die 40 bis 50 Mol-% Fe2O3, bis zu 20 Mol-% CuO und von 0 bis 10 Mol-% Bi2O3 mit NiO und unvermeidbaren Verunreinungen als ausgleichenden Rest umfasst, zu bilden.
Anspruch[en]
A magnetic ferrite film formed on a Si substrate for magnetic devices, wherein the magnetic ferrite film contains CuO and is formed on the surface of the Si substrate through printing and sintering characterized in that the CuO content In the film directly adjacent to the surface of the Si substrate is at most 5 mol%whereas the CuO content in the other parts of the film Is larger than 5 mol% up to at most 20 mol%. The magnetic ferrite film as claimed in claim 1, wherein the areal ratio of the Si-Cu rich phase in the interface between the magnetic film and the Si substrate is at most 50%. The magnetic ferrite film as claimed in claim 1 or claim 2, which is formed by applying a ferrite powder-containing paste onto an Si substrate followed by sintering it. The magnetic ferrite film as claimed In any claim 1 to 3, wherein the sintering is performed at a temperature between 920°C and 1250°C. The magnetic ferrite film as claimed in any claim 1 to 4, which comprises, on average of the entire film, from 40 to 50 mol% of Fe2O3, from 15 to 35 mol% of ZnO, up to 20 mol% of CuO, and from 0 to 10 mol% of Bi2O3 with NiO and inevitable impurities as the balance A magnetic device comprising the magnetic ferrite film of any claim 1 to 5. An electric appliance comprising the magnetic device of claim 6 . A method of forming a magnetic ferrite film on a silicon substrate as claimed in any claim 1 to 5, characterized by the steps of: a) applying a first ferrite layer having a CuO content of not larger than 5 mol% onto the substrate; and b) applying over said first ferrite layer at least one other ferrite layer having : CuO content larger than 5 mol%and up to 20 mol% A method according to claim 8, wherein said step b) comprises sintering to form on the Si substrate a magnetic ferrite film having a mean composition that comprises from 40 to 50 mol% of Fe2O3, up to 20 mol% of CuO, and from 0 to 10 mol% of Bi2O3 with NiO and inevitable impurities as the balance.
Anspruch[fr]
Un film magnétique en ferrite formé sur un substrat en Si pour des dispositifs magnétiques, où le film magnétique en ferrite contient du CuO et est formé sur la surface du substrat en Si au moyen d'une impression ou d'un frittage caractérisé en ce que le contenu en CuO du film directement adjacent à la surface du substrat en Si est au plus 5 % molaires, alors que le contenu en CuO dans les autres parties du film est supérieur à 5 % molaire jusqu'au plus 20 % molaire. Le film magnétique en ferrite selon la revendication 1, où le ratio de surface de la phase riche en Si - Cu dans l'interface entre le film magnétique et le substrat en Si est au plus 50%. Le film magnétique en ferrite selon la revendication 1 ou 2, qui est formé au moyen d'une application d'une pate contenant un poudre de ferrite sur un substrat en Si suivi par son frittage. Le film magnétique en ferrite selon la revendication 1 à 3, où le frittage est effectué à une température entre 920°C et 1250 °C. Le film magnétique en ferrite selon la revendication 1 à 4, comprenant en moyenne sur le film entier, entre 40 et 50 % molaire de Fe2O3, entre 15 et 35 % molaire de ZnO, jusqu'à 20 % molaire de CuO, et entre 0 et 10 % molaire de Bi2O3 avec NiO et des impuretés inévitables comme reste. Un dispositif magnétique comprenant le film magnétique en ferrite selon n'importe lequel des revendications 1 à 5. Appareil électrique comprenant le dispositif magnétique selon la revendication 6. Un procédé de fabrication d'un film magnétique en ferrite sur un substrat en silicium selon n'importe lequel des revendications 1 à 5, caractérisé par les étapes suivantes : a) application d'une première couche de ferrite ayant un contenu en CuO non pas supérieure à 5 % molaire sur le substrat ; et b) application sur ladite première couche de ferrite au moins une autre couche de ferrite ayant un contenu en CuO supérieure à 5 % molaire et jusqu'à 20 % molaire. Un procédé selon la revendication 8, où l'étape b) comprend le frittage pour former , sur le substrat en Si, un film magnétique en ferrite ayant une composition moyenne comprenant entre 40 et 50 % molaire de Fe2O3, jusqu'à 20 % molaire de CuO, et entre 0 et 10 % molaire de Bi2O3 avec NiO et des impuretés inévitables comme reste.






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