EP1178504A1 - Micro component of the micro inductance or micro transformer type - Google Patents

Abstract

The inductive micro component has a metallic coil with a magnetic center (4) and strips (12,13). There is a ferromagnetic material in the center. The center carries an inductive layer (11) generating a magnetic field perpendicular to the solenoid axis.

Description

Technical area

The invention relates to the field of microelectronics, and more specifically in the manufacturing sector of microcomponents, especially intended to be used in radio frequency applications. It concerns more precisely microcomponents such as micro-inductors or micro-transformers equipped with a magnetic core allowing operation at particularly high frequencies.

Previous techniques

As we know, the electronic circuits used for applications radio frequencies, such as in particular mobile telephony, include oscillating circuits including capacitors and inductors.

Given the trend towards miniaturization, it is imperative that the microcomponents such as micro-inductors occupy an increasing volume more reduced, while maintaining a sufficient inductance value and a coefficient high quality.

In addition, the general trend is to increase the frequencies of operation. Thus, we can cite as an example the frequencies used in the new UMTS standards for mobile telephony, which are around 2.4 GigaHertz, by comparison with the frequencies of 900 and 1800 MegaHertz used for the GSM standard.

Increasing operating frequencies poses relative problems to the behavior of magnetic cores of micro-inductors.

Indeed, to obtain a good quality factor, we generally seek to increase the inductance value of the micro-inductance. For this purpose, we choose magnetic materials whose geometry and dimensions allow to have a the highest possible permeability.

However, given the phenomena of gyromagnetism, it is known that the permeability varies with frequency, and more specifically that there is a resonant frequency beyond which an inductor has a capacitive behavior. In other words, a micro-inductor must imperatively be used at frequencies below this resonant frequency.

However, the increase in the frequencies of use therefore comes up against the phenomenon gyromagnetic resonance, which limits for a given geometry the range of frequency in which the inductor can be used optimally.

A problem which the invention proposes to solve is that of limitation the frequency of use inherent in the existence of a phenomenon of gyromagnetism.

Statement of the invention

The invention therefore relates to an inductive microcomponent such as a micro-inductor or a micro-transformer, which has a metallic winding in the form of a solenoid, and a magnetic core including a ribbon in one ferromagnetic material positioned in the center of the solenoid.

According to the invention, this microcomponent is characterized in that the core comprises at least one additional layer parallel to the strip, capable of generating a magnetic field oriented perpendicular to the axis of the solenoid.

In other words, the additional layer associated with the ferromagnetic tape is the seat of a magnetic field which closes by passing through the ribbon, and therefore subjecting the latter to a magnetic field perpendicular to the axis of the solenoid, and therefore generally at the large dimension of the nucleus.

The presence of this additional magnetic field inside the ribbon, oriented parallel to the easy axis of magnetization of the ferromagnetic tape, opposes the rotation of the magnetizations oriented at rest along the easy axis. This is therefore results in a decrease in the magnetic permeability of the tape, and therefore a decrease in the inductance value of the microcomponents; we found that this drawback is offset by the increase in the resonant frequency for the gyromagnetic effect corresponding to the maximum frequency at which the microcomponent retains its inductive behavior.

• M représente le moment magnétique,
• H le champ magnétique dans lequel est plongé ce moment,
• γ la constante gyromagnétique,
• et α le facteur d'amortissement.

The determination of the gyromagnetic resonance frequency involves the Landau-Lifschitz equation which follows: 1 ∂ M γ ∂ t = M ∧ H + α ∂ M γ ms ∂ t ∧ M in which :

• M represents the magnetic moment,
• H the magnetic field in which this moment is plunged,
• γ the gyromagnetic constant,
• and α the damping factor.

To determine the permeability along the difficult axis of the ferromagnetic material, which corresponds to the main axis of the solenoid, it is necessary to determine the different magnetic fields to which the material is subjected. Thus, when a material of a given shape is immersed in a magnetic field (H _ext ), the magnetizations tend to align.

The neutrality of the material is therefore lost, charges appear which create a field opposing the external field, thus reducing the resulting internal field (H _int ). The field opposing the external field is generally called "demagnetizing field" (H _d ), and strongly depends on the geometry. More precisely, we call N the demagnetizing field coefficient such that: H _d = - N M

This coefficient N only depends on the geometry. This demagnetizing field, created by the magnetization components in the direction of the difficult axis decreases the resulting internal field and therefore opposes the passage of flow lines. In other words, this demagnetizing field results in a drop in the permeability.

Thus, taking into account this modeling, we can solve the equation of Landau-Lifschitz to determine, along the difficult axis, the value of the permeability. As we know, magnetic permeability is a complex quantity, in which the real part represents the effective permeability, while the real part imaginary represents losses. So solving these equations gives the values of the real part (µ ') and the imaginary part (µ ") function of the frequency, N, and intrinsic properties of the material.

• N est le coefficient de champ démagnétisant,
• γ est la constante gyromagnétique,
• H_k est la valeur du champ d'anisotropie,
• et M_s est la valeur du moment magnétique à la saturation.

The resonant frequency, for which the value of µ "is maximum is as follows: f res = γ 2π ( H k + NOT .4π M s ) ( H k + 4.π M s ) in which :

• N is the demagnetizing field coefficient,
• γ is the gyromagnetic constant,
• H _k is the value of the anisotropy field,
• and M _s is the value of the magnetic moment at saturation.

We therefore see that the resonant frequency is an increasing function of the value of the anisotropy field which orients the magnetic domains according to the easy axis. So, by subjecting the ferromagnetic core to a field additional thanks to the additional and characteristic layer, we add a additional field to the intrinsic anisotropy field, which increases the effect anisotropy for magnetic domains.

Therefore, the magnetic permeability, illustrating the ease to cause the rotation of the magnetization of the material is reduced, since the magnetic field additional opposes such a phenomenon. In return, the frequency of resonance for the gyromagnetic effect, increasing function of the field value anisotropy, is higher, which allows the use of micro-inductance or of the micro-transformer at higher frequencies.

In practice, the additional magnetic field can be generated either by a additional layer of a so-called hard (magnet) ferromagnetic material, i.e. conductive metal layer intended to be traversed by an electric current.

In the first case, the magnetization of the additional hard layer is chosen perpendicular to the axis of the solenoid.

In practice, provision may be made for interposing or not between the additional layer hard and the ferromagnetic material core a separation layer allowing in particular to limit the effects of magnetic coupling.

Advantageously in practice, two additional layers can be provided. each located on one side of the ferromagnetic tape, so that further increase the value of this additional field added to the field intrinsic anisotropy, and therefore the resonant frequency setting the upper limit at which the inductance can be used.

Advantageously in practice, the hard ferromagnetic material of the layer additional can be chosen from the group comprising alloys of cobalt-platinum or hexaferrites.

Depending on the thickness and the remanent magnetization of the layer additional, you can choose the value of the magnetic field which is added to the intrinsic anisotropy field, and therefore the permeability value of the nucleus. We can thus realize micro-inductances with inductance values predetermined.

In the case where the additional layer is a conductive metallic layer, advantage can be provided to connect it to means making it possible to adjust the intensity and / or shape of the electric current flowing through it. It is so possible to dynamically adjust the value of the magnetic field at saturation, and therefore the magnetic permeability, and as well as the value of the inductance. This arrangement allows for example to dynamically vary the frequency of resonance of a particularly simple oscillating circuit.

In practice, the ferromagnetic tape and the additional conductive layer can be either electrically isolated or electrically connected. For these high frequency applications, the ribbon and additional layers are advantageously isolated.

The geometry of the core is not limited to the simple association of two layers, but we can plan to use several additional layers hard ferromagnetic between which the magnetic tape is interposed or else an additional layer (hard or conductive) sandwiched between two ferromagnetic tapes.

Although not the preferred embodiment, when the material ferromagnetic tape is conductive, we can plan to run it through a current so that a magnetic field is created inside the ribbon. This field produces effects similar to those generated by an additional layer separate.

Brief description of the figures

La figure 1 est une vue de dessus schématique d'une micro-inductance réalisée conformément à l'invention.

La figure 2 est une vue en coupe longitudinale selon le plan II-II' de la figure 1.

La figure 3 est une vue en coupe transversale selon le plan III-III' de la figure 1.

Les figures 4 à 7 sont des vues en coupes analogues à la figure 3, pour différentes variantes de réalisation.

The manner of carrying out the invention as well as the advantages which result therefrom will emerge clearly from the embodiment which follows with the support of the appended figures, in which:

Figure 1 is a schematic top view of a micro-inductor produced according to the invention.

FIG. 2 is a view in longitudinal section along the plane II-II 'of FIG. 1.

Figure 3 is a cross-sectional view along the plane III-III 'of Figure 1.

Figures 4 to 7 are sectional views similar to Figure 3, for different embodiments.

Way of realizing the invention

As already indicated, the invention relates to microcomponents such as micro-inductors or micro-transformers whose magnetic core includes a ribbon of ferromagnetic material and a specific layer which is the source an additional magnetic field added to the field intrinsic anisotropy of the ferromagnetic tape.

This additional layer can be made either from a material ferromagnetic says hard, either from a conductive material, so that when traversed by a current, this layer is the seat of a field magnetic.

In the following description, this second embodiment is described more in detail.

Thus, as illustrated in FIG. 1, a micro-inductance (1) conforming to the invention comprises a metal coil (2) consisting of a plurality of turns (3) wrapped around the magnetic core. More precisely, each turn (3) of the solenoid includes a lower part (5) which is inserted on the surface of the substrate (6), as well as a plurality of arches (7) connecting the ends (8, 9) of the lower parts adjacent (5-5 ').

Thus, to obtain such an inductance, one proceeds to the etching of a plurality of parallel channels (10) on the upper face of an insulating substrate or an insulating layer on a conductive or semiconductor substrate (6). We obtains the lower parts (5) of each turn by electrolytic growth of copper, then planarize the surface of the substrate (6) to obtain a surface finish optimal.

Next, a layer of silica (11) is deposited above the face. upper of the substrate (6), so as to isolate the lower parts (5) of the turns screw materials used for the magnetic core.

The magnetic core (4) is then produced. As already said, multiple architectures can be adopted, and the following description describes in detail a nonlimiting embodiment. The core (4) of Figure 3 therefore comprises two ferromagnetic tapes (12,13) between which a layer is located conductive (14).

More precisely, to produce the layer (12) of ferromagnetic material, several techniques can be used, such as sputtering or electrolytic deposition. Thus, in the second technique, the deposit is ensured electrolytic magnetic material above a growth zone located above the plurality of segments forming the lower parts (5) of the turns. The thickness of the magnetic layer (12) is chosen between 0.1 and 10 micrometers, to obtain sufficient inductance while limiting current phenomena induced.

After having deposited the lower layer (12) of ferromagnetic material, we deposits an insulating layer (15) by sputtering above of the lower layer (12). A conductive layer (14) is subsequently deposited, which can be for example gold. This deposition can take place electrolytically or by sputtering. This conductive layer (14) is in turn covered with an insulating layer (16).

Thereafter, a second ferromagnetic layer (13) is deposited. above the conductive layer (16), in the same way as for the layer (12).

The two ferromagnetic layers (12, 13) are preferably of the same thickness to ensure symmetry around the conductive layer (14).

After having completed the entire magnetic core (4), we proceed to the deposition a layer of silica (22) intended to electrically insulate the magnetic core (4) of the upper part (7) of the turns (2). Subsequently, a deposit is made electrolytic copper to form arches (7) connecting the opposite ends adjacent lower parts (5-5 '), to obtain the microcomponent illustrated in figure 1. Subsequent steps for the creation of connection pads (23, 24), as well as a possible passivation can be carried out.

The magnetic materials used for the core can be relatively varied since they have a strong magnetization and a controlled anisotropy. Thus, it can be crystalline or amorphous materials such as, for example, CoZrNb or other alloys based on cobalt, nickel or iron. Regarding the layer conductive, it can be made of materials with low resistivity such as than copper or gold.

Thus, when the conductive intermediate layer (14) is traversed by a current flowing along the axis (20) of the solenoid, between the studs (26, 27), a field magnetic is generated perpendicular to the axis (20) of the solenoid, forming field lines around the conductive layer (14). This field (represented by arrows) goes through the ferromagnetic layers (12, 13) framing the conductive layer (14). This additional field is added to the anisotropy field intrinsic characteristic of ferromagnetic material. This field therefore opposes the rotation of the magnetizations of the different magnetic domains which are naturally oriented along the easy axis of the ferromagnetic material, i.e. perpendicular to the axis of the solenoid. This opposition to the rotation of magnetizations results in an increase in the value of the magnetic field necessary to obtain saturation, and therefore a decrease in permeability magnetic core.

In addition, and as explained above, the increase in the field of saturation results in an increase in the resonant frequency of the gyromagnetic effect. Increasing this resonant frequency allows therefore to use the microcomponent at higher frequencies than for existing components.

The electric current flowing through the conductive layer (14) can be adjusted to vary the permeability of the magnetic core, and therefore the coefficient component inductance.

Of course, the invention is not limited to the single form described in detail in which the additional magnetic field is obtained by means of a layer additional conductive. Indeed, this additional field can also be obtained by an additional hard ferromagnetic layer, arranged in such a way so that its magnetization is perpendicular to the axis of the solenoid. So as illustrated in FIG. 4, the core comprises an additional layer (32) in a hard ferromagnetic material interposed between two strips of material ferromagnetic (30,31). The field (represented by arrows) generated by the layer (32) closes with the two ribbons (30,31), thus increasing the field intrinsic anisotropy.

The invention is also not limited to the embodiment illustrated in which the core comprises two ferromagnetic layers between which is interposed the additional layer, but other architectures can be envisaged in which the core comprises a single ferromagnetic layer and an additional hard ferromagnetic layer. So, as illustrated in figure 5, the core comprises a ribbon of ferromagnetic material (35) associated with a additional layer (36) of hard ferromagnetic material. The field (represented by arrows) generated by the layer (36) closes with the ribbon (35), increasing thus the intrinsic anisotropy field of the layer (35). This layer in ferromagnetic material can be replaced by a conductive layer, which when traversed by a current produces a field in the layer ferromagnetic (35). The additional layer can be above or below the ferromagnetic tape, depending on thicknesses and manufacturing process selected.

Other structures are also covered by the invention, such as those comprising a set of several ferromagnetic layers associated with several additional layers, ferromagnetic or conductive. So like illustrated in Figure 6, the core may include a ribbon (40) of material ferromagnetic, interposed between two hard ferromagnetic layers (41,42). The fields (represented by arrows) generated by the additional layers are close in the ribbon (40), thereby producing the desired effect. As illustrated in Figure 7, these two hard ferromagnetic layers can be replaced by two conductive layers (45,46), traversed by identical currents, but of opposite directions, so that the fields (represented by arrows) that it generates have the same direction when they close in the ribbon (40).

Furthermore, although the invention is described in more detail with regard to micro-inductors, it goes without saying that the realization of micro-transformers, with two windings wound on a common core, is also covered by the invention.

It appears from the above that the microcomponents according to the invention have multiple advantages including increasing the frequency maximum operating compared to microcomponents of dimension and of identical materials, as well as a possibility to vary dynamically magnetic permeability, and therefore the value of the inductance.

These microcomponents find a very particular application in the application of radio frequency and in particular in mobile radio telephony.

Claims (10)

Inductive micro-component (1), such as micro-inductance or microtransformer, comprising a metal coil (2) having the shape of a solenoid, and a magnetic core (4) including a ribbon (12, 13) made of a ferromagnetic material, positioned in the center of the solenoid (2), characterized in that the core (4) comprises at least one additional layer (14) parallel to the strip (12, 13), capable of generating a magnetic field oriented perpendicular to the axis (20) solenoid (2). Microcomponent according to claim 1, characterized in that the additional layer (36) is made of a ferromagnetic material. Microcomponent according to claim 2, characterized in that it comprises a separating layer (15,16) between the ribbon (12, 13) and the additional layer (14). Microcomponent according to claim 1, characterized in that it comprises two additional layers each situated on one side of the strip. Microcomponent according to claim 2, characterized in that the ferromagnetic material of the additional layer is chosen from the group comprising: cobalt platinum alloys and hexaferrites. Microcomponent according to claim 1, characterized in that the additional layer (14) is a conductive metallic layer, intended to be traversed by an electric current. Microcomponent according to claim 6, characterized in that the additional layer (14) is connected to means making it possible to adjust the intensity and / or the shape of the electric current flowing through it. Microcomponent according to claim 6, characterized in that the tape and the additional layer are electrically insulated. Microcomponent according to claim 6, characterized in that the strip (12, 13) and the additional layer (14) are electrically connected. Microcomponent according to claim 6, characterized in that it comprises several ribbons (12, 13) between which are interposed additional conductive metallic layers (14).

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