FR2907589A1 - Integrated micro-induction coil for e.g. power electronics application, has disjointed loops constituting winding around core, where core has four parallel branches that are enclosed by winding and have ends connected by respective bases - Google Patents

Abstract

The coil has a set of disjointed loops (2) constituting a solenoid winding around a closed magnetic core (1), where the loops are arranged in series and the coil is of rectangular or circular shape. The core has four parallel branches (3a-3d) that are enclosed by the winding. The branches have ends that are connected by respective bases (6, 7), where thickness of the branches is different from thickness of the bases. Each loop has lower and upper flat sections (8, 9) in respective lower and upper planes.

Description

1 Integrated micro-inductance comprising a closed magnetic core of the type

  TECHNICAL FIELD OF THE INVENTION The invention relates to an integrated micro-inductance comprising a closed magnetic core and a plurality of disjoint turns constituting a winding around the magnetic core. STATE OF THE ART The invention is in line with the theme of integrated micro-reactors for applications in power electronics. It can, more generally, apply to all inductive systems integrated or not (inductors, transformers, magnetic recording heads, actuators, sensors, etc ...) requiring a high density of electrical power. Micro-inductances of various types have existed for many years, using spiral or solenoid windings. However, the discrete components remain mostly used in applications using high power densities because they offer a better compromise between inductance and saturation current. A spiral-type micro-inductance with magnetic plane is easy to integrate and allows to work with strong currents. However, this type of device becomes very cumbersome if one targets high values of inductance (L of the order of pH), because it takes a high number of turns of spiral. In addition, the resistance of such devices is important. 2907589 2 Toroidal integrated micro-inductors with solenoid winding, as well as their meander enhancements (see Integrated Electroplated Micromachined Magnetic Devices Using Low Temperature Manufacturing 5 Processes by JYPark et al., IEEE Transactions on Electronics Packaging Manufacturing, Vol. 23, n .1, 2000), are directly inspired by the discrete components and offer the best possible compromise between resistance and inductance level, because one approaches the ideal case of the infinite solenoid. However, simulations show that the magnetic flux inside the core is distributed very inhomogeneously. The magnetic field is more intense along the shorter field lines. The zones of the magnetic core subjected to the most intense fields are very quickly saturated, causing a decrease of the inductance from weak currents, whereas other zones are subjected to much weaker fields and participate little or not in inductive phenomenon, that is to say they have no contribution to the value of the inductance. The useful areas of the magnetic core are therefore very quickly saturated while other areas remain unsolicited.

  In addition, the maximum power passing through an inductor is determined by the volume of magnetic material used in the case of an integrated component. This volume is determined by the thickness of magnetic material (thicknesses less than 100 microns for integrated components) and the area occupied by this magnetic core. However, in the case of a toroidal core, a large part of the surface of the chip (in the center) is not used because it is empty of magnetic material. Transformers and inductors with E-shaped or E-1 magnetic core are widely used in electrical engineering, mainly in discrete transformers (and in discrete DC / DC type devices) to facilitate assembly and winding of inductors , or else to be able to play on the conversion factors between the three windings of each branch, or on the effects of mutual inductances between the windings dictincs of each branch (see the article New Magnetic Structures for Switching Converters of S. Cuk, IEEE Transactions on Magnetics, Vol MAG-19, No. 2, 1983). In these devices, the winding is not continuous from one branch to the other, but made by separate wires. Most of the micro-inductors used on the market are discrete components manufactured by micromechanical processes of micro machining, gluing, micro-winding, etc ... These processes are heavy to implement, individually treated, not very flexible in terms of design and greatly limit the miniaturization of power circuits. In particular, the thickness of the discrete micro-inductors (typically greater than 0.5 mm) does not allow an appropriate packaging in the power supply circuits currently used for mobile telephony, for example. The manufacturing techniques used in microelectronics allow a much greater flexibility in the implementation of different designs, provide a collective treatment and are compatible with the idea of miniaturization because the thickness (including substrate) can easily be lower at 300 pm). However, they are poorly suited to deposition of high thicknesses (greater than 10 μm) of conductive, magnetic or dielectric materials and to their etching after photolithography.

For integrated components, there are constraints of technological achievement. Indeed, deposits of conductive layers having a thickness greater than 100 microns are currently not feasible in a standard industrial process.

The Numerical Inductor Optimization article by A. von der Weth et al. (Japan Magn Magn., Vol.2, No.5, pp.361-366, 2002) discloses a micro-inductance with an open multi-branch type magnetic circuit. A plurality of turns disjoined from each other constitutes a winding around the branches of the magnetic core. For these devices, it is sought to increase the level of inductance and to minimize losses. The integrated micro-inductors generally have an inductance which decreases greatly when the current applied to the turns of the micro-inductor is increased, even for weak currents, which makes it necessary to use discrete non-integrated inductors, in certain cases . OBJECT OF THE INVENTION The object of the invention is to improve the performance of a micro-inductor, in particular the stability of the value of the inductance as a function of the current, while increasing its compactness. For a given size, this makes it possible to improve the compromise between the level of inductance and the saturation current. According to the invention, this object is achieved by the fact that the magnetic core comprises at least four substantially parallel branches surrounded by said coil, each of the branches having first and second ends, the first ends of the branches being connected by a first base and the second ends of the branches being connected by a second base. According to a preferred embodiment of the invention, the branches are arranged in a first plane and the first and second bases are arranged in a second plane parallel to the first plane. Thus, the branches may in particular have a thickness different from the thickness of the first and second bases. The micro-inductance preferably comprises between four and eight branches. BRIEF DESCRIPTION OF THE DRAWINGS Other advantages and features will emerge more clearly from the following description of particular embodiments of the invention given by way of nonlimiting example and represented in the accompanying drawings, in which: FIG. , in perspective view, a particular embodiment of an integrated micro-inductor according to the invention, FIGS. 2 to 8 represent, in perspective view, seven particular embodiments of a magnetic core of a micro integrated inductance according to the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION FIG. 1 shows an integrated micro-inductance comprising a closed magnetic core 1 and a plurality of disjointed turns 2, constituting a continuous winding around the magnetic core 1 .

The magnetic core 1 has four substantially parallel branches 3 (3a, 3b, 3c, 3d). The branches 3 each have a first end 4 and a second end 5. The first ends 4 of the branches 3 are connected by a first base 6 and the second ends 5 of the branches 3 are connected by a second base 7.

The micro-inductance with a closed magnetic core and having at least four substantially parallel branches 3 makes it possible, for a given number of winding turns, to obtain a higher surface density of inductance and a higher saturation current. as the inductor in the form of torus or meanders. The micro-inductance according to the invention makes it possible to more effectively channel the magnetic field lines inside the core. The magnetic flux generated by the winding is added inside each branch. For a predetermined available surface, on a substrate or on a chip, the characteristics of the inductance of the micro-inductor can be optimized when four or substantially parallel branches 3 are used. The magnetostatic energy contained in the magnetic core is thus greater than that contained in a toroidal core or 15 meanders constant space, that is to say for chips of the same size. Thus, from four branches, it can be seen that the inductance as a function of the current flowing through the turns 2 is more stable in a range of currents typically used than an integrated toroidal inductance. This is due in particular to the fact that the magnetic flux density reaches a more homogeneous distribution in the core 1, ie the magnetic field excites the volume of available magnetic material (in particular the intermediate branches 3b and 3c of the core 1), whereas in an annular rectangular micro-inductor, for example, the magnetic field is only concentrated in the inner corners and edges of the magnetic core. Thus, the micro-inductance makes it possible to optimize the compromise between the level of inductance and the saturation current of an inductive system. In the particular embodiment shown in FIG. 1, each turn 2 comprises a lower plane section 8 in a lower plane, an upper plane section 9 in an upper plane and two rising sections 10.

The lower and upper planes are parallel to the plane of the magnetic core 1. In the particular embodiment shown in FIG. 1, all the turns corresponding to a predetermined branch (for example the branch 3a) are directly connected in series, then all the turns corresponding to another branch (for example the adjacent branch 3b) are also connected directly in series, as in the case of a solenoid winding.

It should be noted that the elements constituting a turn (the lower plane section 8, the upper plane section 9 and the two rising sections 10) are not necessarily connected to each other so as to form a loop, for example in the case of a conventional solenoid winding. Indeed, the plane sections 8 and 9 may belong to distinct electrical conductors 15, each electrical conductor passing from the lower plane for a predetermined branch to the upper plane for an adjacent branch and vice versa (by interlacing in analogy with the weave of a weave ), the set of turns 2 constituting a single winding and, thus, a single inductor.

As shown in FIG. 1, the winding comprises, for the electrical connection, a single electrical input 12 and a single electrical output 13, so as to constitute a single winding. All the turns 2 are connected in series between the input 12 and the output 13. This is therefore not a question of several separate windings, for example, in the case of a primary winding and a secondary winding. a transformer or in the case of several windings connected in parallel with a point common to the ground.

The use of more than four branches makes it possible to improve the characteristics (compromise between inductance, current and power 2907589 8) of the micro-inductance, however, often a large number of branches can not be realized because the place available on the substrate or the chip is not sufficient. The magnetic core 1 preferably comprises between four and eight branches, for example six branches 35 as shown in FIG. 3. The magnetic core 1 comprises in particular eight branches in the case where the space requirements of the device allow it. As illustrated in FIGS. 1 to 3, all the branches 3 preferably have the same width and all the gaps between two adjacent branches are equal. However, if necessary, an adaptation of the widths of the branches 3 is possible. Thus, in FIG. 4, the branches 3 have different widths W1, W2, W3 and W4. Deviations 11, 12 and 13 may also be different. In fact, in certain cases, the geometrical shape of the core must be adapted when space constraints or spatial constraints require it. The sizing of the magnetic core 1 can be done according to the method illustrated in FIG. 4: the dimension C defining the maximum size of the magnetic core 1 is defined. The minimum spacing IMIN between the branches 3 with respect to the margins of acceptable technological achievements and the winding dimensions around each leg 3. A maximum spacing IMAX may be provided to take account of the maximum bulk of the magnetic core 1. The maximum spacing IMAX can be determined from the dimension C , the minimum width WMIN of each branch and the minimum spacing IMIN using the expression IMAX = CN * WMIN- (N-1) * IMIN, where N is the number of branches. The EMAG thickness of magnetic material is defined as a compromise between difficulty of realization and the level of inductance desired for a given C 30 coast. The maximum width WMAX of each branch 3 is determined by the required operating frequency or by technological constraints. Thus, the maximum width WMAX must be less than the wavelength X corresponding to the operating frequency, for example WMAX is of the order of J4 or X / 10. The minimum width WMIN of each branch is possibly determined by the structure in magnetic domains of the material or by the realization constraints that it is desired to obtain. The number of branches N is chosen according to all the other parameters. The widths W1 to W4 of the branches 3 and the widths W5 and W6 of the bases 6 and 7 may be different, but must all be between WMIN and WMAX. Similarly, the gaps 11, 12 and 13 must be between IMIN and IMAX. Moreover, the minimum width WMIN of each branch must be greater than the thickness of the magnetic material of the branch. The minimum spacing IMIN must also be greater than the thickness of the magnetic material of the branch and preferably at least three times greater for a braided type winding and at least five times greater for non-braided windings as shown in FIG. Figure 1. One or more air gaps may optionally cut the magnetic core 1 to increase the reluctance of the magnetic circuit. The magnetic core 1 shown in FIG. 5 comprises a number of small air gaps 11 (at least a factor of 1/10 between the dimension of the air gap and the total length of the magnetic circuit). The air gaps can be arranged in the branches 3 and in the bases 6 and 7.

In FIG. 6, the branches 3 are arranged in a first plane and the bases 6 and 7 are arranged in a second plane parallel to the first plane. The branches and the bases are respectively constituted by two superimposed structured magnetic layers. Thus, the bases 6 and 7 may have a thickness different from that of the branches 3, or a preferential direction of propagation of the magnetic flux in dynamics (called axis of difficult magnetization) different from the branches 3 (for example at 2907589 900). The bases and branches may also have the same thickness, especially when a single structured magnetic layer is used as in the case of Figure 2.

As shown in FIGS. 1 to 6, the branches 3 are preferably substantially parallel and the first and second bases 6 and 7 and the branches 3 each have a rectangular shape. However, according to the needs, other more complex shapes may be envisaged, for example shapes having variable widths, irregular shapes, curved or bent, etc. The skilled person determines these forms using software such as the Flux software from the company Cedrat or the Maxwell software from Ansoft. In Figure 7, for example, the set of first and second bases 6 and 7 and two outer branches 3a, 3d form a ring, traversed by two inner branches 3b, 3c. In FIG. 8, the first and second bases 6 and 7 and branches 3 have trapezoidal or polygonal shapes. For integrated components using conventional micro-fabrication techniques, the micro-inductance presents no additional manufacturing difficulties compared to conventional pre-existing systems. For the magnetic core 1, high permeability magnetic materials (greater than 10), typically iron (Fe) and / or nickel (Ni) and / or cobalt (Co) alloys, which can contain one or more of aluminum, Al, Si, tantalum, Hf, N, O, and bor The core may be heterogeneous and consist of several ferromagnetic and conductive or dielectric (non-magnetic) or antiferromagnetic layers. In particular, the core may consist of alternating magnetic layers and intermediate layers, for example a stack comprising two magnetic layers separated by an intermediate layer. The intermediate layers may, for example, be metal (Cu copper, Ti titanium or Ruthenium Ru, for example) or an insulating material such as silicon oxide SiO 2 or aluminum oxide Al 2 O 3, for example. The intermediate layers may also be constituted by antiferromagnetic materials such as nickel oxide NiO or manganese alloys (Mn) comprising nickel (NiMn), iridium (Mn) or platinum (PtMn). Microinductance is not limited in its frequency of use, and may be suitable for high frequency uses, which still require more power. One can then very well imagine such components working in the range of microwaves and replacing integrated or discrete inductances, with or without magnetic material, which are usually used. We then find applications of the filtering type, impedance matching, etc.

Claims (10)

claims   1. Integrated micro-inductance comprising a closed magnetic core (1) and a plurality of disjoint turns (2) constituting a coil around the magnetic core (1), a micro-inductance characterized in that the magnetic core (1) comprises at least four substantially parallel branches (3) surrounded by said winding, each of the branches (3) having a first (4) and a second (5) end, the first ends (4) of the branches (3) being connected by a first base ( 6) and the second ends (5) of the legs (3) being connected by a second base (7).   Micro-inductor according to claim 1, characterized in that each turn (2) has a lower plane section (8) in a lower plane, an upper plane section (9) in an upper plane and two rising sections (10). .   3. Micro-inductor according to one of claims 1 and 2, characterized in that the winding comprises a single inlet (12) and a single electrical outlet (13) electric.   4. Micro-inductor according to any one of claims 1 to 3, characterized in that all the turns (2) are connected in series.   5. Micro-inductor according to any one of claims 1 to 4, characterized in that the branches (3) are arranged in a first plane and the bases (6, 7) are arranged in a second plane parallel to the foreground .   Micro-inductor according to one of Claims 1 to 5, characterized in that the legs (3) have a thickness different from the thickness of the bases (6,   7). 7. Micro-inductor according to any one of claims 1 to 6, characterized in that the branches (3) have a preferential direction of propagation of the magnetic flux in dynamic different from that of the bases 5 (6, 7). .   8. Micro-inductor according to any one of claims 1 to 7, characterized in that the magnetic core (1) comprises at least one gap (11).   9. Micro-inductor according to any one of claims 1 to 8, characterized in that all the branches (3) have the same width. 1O.Micro-inductor according to any one of claims 1 to 9, characterized in that all the deviations (I1, 12, 13) between two adjacent branches (3) are equal. 11. Micro-inductor according to any one of claims 1 to 10, characterized in that it comprises between four and eight branches (3). 10 20