The invention relates to an inductive micro-device comprising a rectilinear solenoid winding comprising a plurality of disjointed rectangular turns each having predetermined dimensions.
The invention applies in particular to all inductive systems, either integrated or not, of the type involving inductors, transformers, magnetic recording heads, actuators, sensors etc. requiring low losses or a very homogeneous magnetic flux density. The invention applies more particularly to integrated micro-inductors.
Integrated micro-inductors with different types of winding, for example of the solenoid or spiral type etc., have existed for a large number of years now. In a spiral winding, the turns located at the center of the winding generally contribute more to high-frequency losses than the other turns. These losses are conventionally proportional to the thickness of the turn and to the cube of its width. New forms of spirals have been designed and proposed, but their gains prove to be limited.
A conventional solenoid winding presents the advantage of having a periodic structure, which limits proximity effects naturally. However, at the edges of the solenoid, the proximity effects remain very high. Furthermore, inside the solenoid, the magnetic flux may be fairly inhomogeneous, which may cause problems in the presence of magnetic material.
For example purposes,
However, the proximity effects in the winding, and in particular at the level of the internal turns, are very high. These effects can moreover be further increased by the presence of a high-permeability magnetic material, in particular as described in the article “Investigation of anomalous losses in thick Cu ferromagnetic spiral inductors” by B. Viala et al. (IEEE Trans. Magnetics, vol. 41, n° 10, pp. 3583-3585, October 2005) and in the article “Analysis of current crowding effects in multiturn spiral inductors” by W. B. Kuhn et al. (IEEE Trans. Microwave Theory and Techniques, vol. 49, n° 1, pp 31-38, January 2001).
To reduce the effect of losses described above, an inductance 3 in the form of a planar spiral 4 with a variable width of turn, as represented in
In
In
However, for turns 9 at the edge of solenoid 8, there is not this compensation. Furthermore, inside a turn 9, a proximity effect exists between the bottom and top parts of the turn, and these effects can be further increased in the presence of a magnetic material. The magnetic field is moreover inhomogeneous inside solenoid 8, which may cause problems as far as current strength is concerned when a magnetic core is used.
If areas of the magnetic core see a more intense magnetic field than others, they will in fact be easily saturated and inductor 7 will be very sensitive to the level of the current flowing through winding 8. Furthermore, the parts of the core seeing a very weak magnetic field will be little solicited and will only participate to a small extent in inductance. Consequently, the trade-off between inductance and current strength will be far from being optimal.
Conventionally, as represented in
Winding 10 is also defined by the gap INT between two adjacent turns 11 (
However, although this conventional configuration of rectilinear solenoid winding 10 is easy to implement, the magnetic field remains non-homogeneous.
The object of the invention is to remedy all the shortcomings set out above and to provide an inductive micro-device having a winding of solenoid type that is easy to implement, that is able to be used for any type of application and that enables proximity effects to be reduced, high-frequency losses to be reduced and a homogeneous magnetic flux to be obtained all along the solenoid winding.
According to the invention, this object is achieved by the appended claims, and more particularly by the fact that one of the dimensions of the turns is variable and determined individually for each turn according to its position along the winding and to predetermined magnetic characteristics of the winding.
Other advantages and features will become more clearly apparent from the following description of particular embodiments of the invention given for non-restrictive example purposes only and represented in the appended drawings in which:
a to 5c respectively represent a front view in longitudinal cross-section, a top view and a side view in transverse cross-section of a particular embodiment of a rectilinear solenoid winding with a rectangular transverse cross-section according to the prior art.
a and 6b respectively represent a front view in longitudinal cross-section and a top view of a particular embodiment of a rectilinear solenoid winding with a rectangular transverse cross-section according to the invention.
a to 7c very schematically represent alternative embodiments of the solenoid winding according to
a and 9b are graphs illustrating, in top view, the form of the winding of certain points of the graph according to
With reference to
The general principle of the invention is illustrated in
In
In
In the same way, magnetic core 15 therefore comprises five different sections each associated with a turn 14 of winding 13. The sections are defined by their width WMAG, their length LMAG and their thickness EMAG. The sections are for example substantially flat and are joined by section transition zones which are for example substantially trapezoid. In
Variation of the dimensions of magnetic core 15 associated with solenoid winding 13 is determined according to the dimensions of associated turns 14 or independently according to the position of the sections of magnetic core 15 along solenoid winding 13 and according to the magnetic characteristics required for solenoid winding 13.
This optimization of the dimensions of each turn 14 of winding 13 and the dimensions of each section of associated magnetic core 15 therefore has the purpose of improving not only the operation of solenoid winding 13 itself, but also of improving the performances of the different inductive systems incorporating such a solenoid winding 13.
Solenoid winding 13 according to the invention thereby enables a maximum quality factor or a substantially homogeneous magnetic field to be obtained, in particular by reducing the proximity effects, and thereby proposes a generic design solution for any type of inductive component with or without a magnetic core.
In the alternative embodiments represented in
In the particular embodiment represented in
In
In
Furthermore, in the alternative embodiments represented in
Furthermore, in the alternative embodiments represented in
Dimensioning and calculation of the dimensions of each turn of the winding will be described in greater detail with regard to
In general manner, to simplify calculations, EMAG, WMAG (in the case where the winding is associated with a magnetic core), ISOL, INT and EBOB will be considered to be constant. The optimum trade-off for determining the shape of the turns depends on complex phenomena, in particular on induced currents, capacitive effects, non-linearity and non-homogeneity of the magnetic material forming the magnetic core if applicable, and on the targeted work frequency. It is therefore necessary to have recourse to optimization algorithms, possibly coupled with analytical or numerical design models.
In a first example of two-dimensional dimensioning of a solenoid winding according to the invention, to optimize in particular the trade-off between inductance and saturation current, taking as hypothesis a symmetrical solenoid winding with five turns, without a magnetic core, produced using planar technology, the following geometric parameters are to be taken into account:
WBOBwith i={1,2,3}, with by symmetry WBOB1=WBOB5 and WBOB2=WBOB4.
INT, EBOB and ISOL are fixed by technological constraints, for example, at respectively 10 μm, 5 μm and 40 μm.
The length of a turn LBOB does not play any part in two-dimensional dimensioning
There is therefore a total of three independent geometric parameters, i.e. WBOB1, WBOB2 and WBOB3. These geometric parameters are moreover subjected to constraints linked to the dimensions of the winding. Considering, in this first particular calculation example, that widths WBOBi follow a first-term geometric progression WBOB3 corresponding to the width of the central turn, and of ratio Q, i.e. WBOB2=Q×WBOB3 and WBOB1=Q2×WBOB3, only Q therefore remains to be determined, as WBOB3 is determined according to the predefined maximum length LMAX=100 μm of the winding, with the formula:
The standard deviation σ of the magnetic field inside the space of height EMAG=5 μm and length LMAX, in the heart of the solenoid and corresponding to the space occupied by a magnetic core if present, is calculated for example from Biot and Savart's law, according to the following equation:
The above calculations then enable the influence of ratio Q on the magnetic flux homogeneity to be highlighted. As represented on the graph of
In a second particular example of dimensioning of a solenoid winding according to the invention, it is possible to perform three-dimensional dimensioning for optimization of the quality factor. Still considering a symmetrical solenoid winding with five turns, without a magnetic core, made using planar technology and which has to fit in a square of predetermined size LMAX=200 μm, the following geometric parameters are to be taken into account:
WBOBi with i={1, 2, 3}, with by symmetry WBOB1=WBOB5 and WBOB2=WBOB4.
Widths WBOBfollow a geometric progression of ratio QW and of first term WBOB3, preferably calculated as in the previous example.
LBOBwith i={1, 2, 3}, with by symmetry LBOB1=LBOB5 and LBOB2=LBOB4.
Lengths LBOBfollow a geometric progression of ratio QL and of first term LBOB3=LMAX.
INT is fixed at 10 μm.
EBOB is fixed at 5 μm, so as to limit skin effects.
ISOL is fixed at 40 μm.
A combination of two parameters, i.e. QW and QL, therefore has to be optimized this time. A quick method for calculating the quality factor is preferably used. In particular Kuhn's method, as described in the article “Analysis of current crowding effects in multiturn spiral inductors” by W. B. Kuhn et al. (IEEE Trans. Microwave Theory and Techniques, vol. 49, n° 1, pp. 31-38, January 2001), enables losses by proximity effects to be calculated. The inductive field can be calculated by Biot and Savart's law. The losses by skin effect can be calculated using Press's two-dimensional approach, as described in particular in his article “Resistance and reactance of massed rectangular conductor” (Phys. Review, vol. VIII, n° 4, p. 417, 1916), the capacitive effects being ignored and the inductance being calculated according to the numerical calculation of the magnetic flux.
It is then possible to calculate an approximate value of the quality factor, which can then be used for determining the optimized dimensions of the winding turns. As represented on the graph of
Indeed, on reading
In another example of dimensioning of a solenoid winding 13 according to the invention, an arithmetic progression can be used to characterize the variation of the dimensions of the turns.
Such a solenoid winding as described above, with optimized shape and dimensions of turns by means of the above calculations, therefore enables the best possible magnetic flux distribution to be obtained by optimizing each section of the winding individually according to the required result. It also enables a maximum quality factor and/or a homogeneous magnetic field to be obtained and enables the performances of inductive systems using such a solenoid winding to be significantly improved.
The solenoid winding according to the invention applies more particularly, without frequency or power limitation, to all inductive systems equipped with a solenoid winding with or without a magnetic core, i.e.:
inductors and transformers,
magnetic recording heads for data storage,
inductive sensors, such as “fluxgates” or “permeameters”,
inductive motors and actuators,
field-generating coils.
For example, to produce a permeameter, such a solenoid winding presents the twofold advantage of generating more homogeneous fields and of being less sensitive to proximity effects. Such a winding therefore enables finer measurements of the response of magnetic materials according to the frequency and the magnetic field by the disturbance method.
To achieve such a solenoid winding, technologies used for producing microsystems can be used, in the case where thickness EBOB of the turns and height of turn ISOL are constant along the winding. For example, a large number of manufacturing methods based on techniques for producing integrated magnetic recording heads are possible. Slightly more complex technologies can be implemented in the case where thickness EBOB and height of turn ISOL are variable.
An example of a method for producing a solenoid winding using a “microsystems” technology can comprise the following steps. A first deposition of a conducting material is performed to form the bottom part of the winding, for example by a damascene electrolysis method. Then a first insulating material is deposited.
One or more depositions of magnetic materials (and non-magnetic materials in the case of producing a laminated core) are then made for formation of a magnetic core. Then one or more lithography and etching steps of the core are performed.
A second deposition of insulating material is then performed, and lithography and etching steps of vias in the two insulator layers are performed to be able to close the winding turns. Finally, a second deposition of conducting material is performed to form the top part of the winding.
Such a production method of the “microsystems” type in particular enables a solenoid winding to be obtained quickly and easily with a great degree of freedom as to the choice of the dimensions of the turns, in particular length LBOB, width WBOB, and spacing INT between turns, which is much more difficult to achieve with a micromechanics method, i.e. a method based on winding a wire.
The invention is not limited to the different embodiments described above. The solenoid winding according to the invention can comprise any number of turns, provided that they present at least one variable dimension along the winding, according to the position of the turn along the winding and the magnetic constraints required of the winding.
In general manner, whatever the variation of the dimensions of the turns, the turns with the largest dimensions should advantageously be placed at the center of the winding.
Other examples of dimensioning and calculation of the optimal form of the solenoid winding can take additional production constraints into account. The bottom part of the solenoid winding can for example not have the same thickness as the top part and the solenoid winding can for example not be symmetrical. In these cases, the number of parameters to be taken into account will be superior. The same will be true of the magnetic core at the heart of the solenoid is not centered with respect to the latter.
With reference to the first dimensioning example (
In other dimensioning examples (not shown), optimization can be performed with less constant preset dimensions. More complex optimization algorithms can then be used, such as genetic algorithms, with for example the Matlab (registered trademark) or Optimetrics (registered trademark) modeling and simulation software, which provide a wide range of constrained or non-constrained optimization methods.
In a more general case, it is possible to use numerical computing software using for example the finite-elements method to calculate the parameters to be optimized more precisely.
Number | Date | Country | Kind |
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0610521 | Dec 2006 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FR2007/001967 | 11/30/2007 | WO | 00 | 5/8/2009 |