EP1301931A1

EP1301931A1 - I-inductor as a high-frequency microinductor

Info

Publication number: EP1301931A1
Application number: EP01969335A
Authority: EP
Inventors: Axel Von Der Weth; Klaus Seemann; Immanuel Fergen
Original assignee: Forschungszentrum Karlsruhe GmbH
Current assignee: Karlsruher Institut fuer Technologie KIT
Priority date: 2000-07-14
Filing date: 2001-07-04
Publication date: 2003-04-16
Also published as: US20030160675A1; WO2002007172A1; US6788183B2

Abstract

An I-inductor for high-frequency technology or microwave technology consists of two cores of the same kind which lie parallel to each other in relation to their longitudinal axes, in such a way that a gap is formed. A solenoidal coil winding is arranged on each core in such a way that when a high-frequency current passes through, a magnetic circuit is produced through the two cores and over the gap in the respective end area of the arrangement. The windings that form the magnetic field are of the same type. In principal, magnetically isotropic material can be used as the core material. However, the technical microwave effect can only be produced in a technically applicable manner with magnetically anisotropic material. The preferred magnetic direction runs in the direction of the longitudinal axis of the respective core.

Description

I-inductor as a high-frequency micro-inductor

The invention relates to an I-inductor, which is a passive magnetic component, a choke.

Using an isotropic magnetically permeable material, the inductor is known as a macroscopic component from transformer technology. He is also known as an RF microinducer for microsystem technology or integrated circuit technology in on-die design (on die = sitting on a chip or a substrate), in which materials with a uniaxial, uniaxial, Use anisotropy to be effective even at high frequencies.

The shape of the magnetically flowing parts results in a reduction in the fields emerging from the component, which greatly reduces the formation of shielding currents in carrier devices for the component or electromagnetic interference in neighboring assemblies. The arrangement of an I-inductor is comparatively compact, so that parasitic capacitances can be kept small. By skillfully conditioning and utilizing the surface, resistance-reducing conductor arrangements can be used, which enable the quality to be increased.

Toroidal choke or toroidal microinductors are similar in their structure and mode of action. However, it can only be constructed with isotropic materials. Magnetic materials with uniaxial anisotropy, which is uniaxial in technical usage, cannot be used. According to the current state of material development, isotropic magnetic materials are no longer suitable for the frequency range above 1 GHz [I]. The assembly also includes solenoids or solenoids. Different versions are known:

In microsystem technology, the solenoid is already used as a planar coil - the coil axis is perpendicular to the substrate. These are only suitable for high frequencies to a limited extent, since shielding currents in the substrate, which reduce the inductance, are excited. These components are of low quality when used in high-frequency technology.

Since the arrangement is not very efficient, especially when using high frequencies, the size of the component increases, which results in an increase in parasitic capacitances. The inductance can be increased by using additional magnetic layers on the end faces of the planar coil, but the cutoff frequency of the coil then drops. An increase in quality by using wider conductor elements in a planar coil is only possible in a small area due to the increase in the area then required [II]. Above 0.1 GHz, this setup is uninteresting due to excessive capacity and eddy current problems and only works with magnetically isotropic materials.

Another group are solenoids, whose coil axis is parallel to the substrate. These are also of limited suitability for the high frequency range due to the excitation of shielding currents in the substrate, since the stray field emerges at the end faces. However, a core made of a material with magnetic uniaxial anisotropy can be used to increase the inductance [III].

Strip lines are also used as inductors. Their achievable quality is in the frequency range mentioned because of the wrestle inductance too low for technical application. To increase the quality, the conductor can be surrounded with a magnetic material. This solution is already used as a macroscopic component with isotropic magnetic materials and discussed in the literature as a microinductor application [IV]. Since, for example, the shape anisotropy of thin layers is not taken into account here and the conditions used are greatly simplified, the application in microsystem technology is rather questionable. The arrangement leads to a considerable excitation of shielding currents in the substrate, which complicates the industrial high-frequency application. Since considerable stray fields can be expected, this must also be taken into account when designing the surrounding electromagnetic assemblies.

To summarize the known relevant prior art:

Toroidal chokes made of materials with magnetically uniaxial anisotropy are ineffective. Magnetic isotropic materials cannot be used for the intended frequency range.

Solenoids are not suitable because of the stray fields that cause shielding currents and thus disturbances in neighboring assemblies.

Strip lines have too little inductance or too high parasitic capacitance.

All of these shortcomings lead to the task on which the invention is based, namely to provide an economically and for industrial production concept of high-performance inductors. The object is achieved by an I-inductor according to the features of claim 1.

The I-inductor consists of at least two band-shaped bodies / cores made of magnetically permeable material which are of equal length and which are necessary for the intended magnetic flux through them in a rectangular delimiting plane with a gap formation, band-shaped, parallel to one another with their respective longitudinal axis. These bodies / cores are provided with at least one winding in such a way that when the winding is loaded, the magnetic field generated by the winding in the associated body / core is strengthened and not weakened by the magnetic field generated in the associated winding of the winding in the immediately adjacent body / core. As a result, the magnetic flux runs completely or virtually completely in the magnetic material and passes into the adjacent body at the winding-free gaps in the end region.

Claim 2 describes the material of the body / core as magnetically isotropic. Different in claim 3, where it is specified as unidirectional or uniaxial magnetic anisotropic.

The geometric relation of the two outer bodies / cores of the arrangement to the ones in between is expressed in claim 4. The two outer ones are of equal width and the ones in between are at least as wide.

In the claims 5 to 8 expedient winding techniques and forms are described. Thus, the respective winding of one solenoid per body / core is in claim 5. In claim 6, the turns of a winding or windings with the bodies / cores form a woven structure. A turn or the turns can also consist of a strip conductor at both ends forms a connection lug for "the external connection (claim 7). In claim 8, the windings of the winding consist of band-shaped square elements, namely in the case of:

- Only two adjacent bodies / cores of the same trapezoidal shape, with two trapezoidal elements in the gap between the two bodies / cores with the shorter of the two parallel trapezoidal sides and along the outer longitudinal edge of the two bodies / cores with the longer of the two parallel trapezoidal sides string together and make electrical contact;

- More than two adjacent bodies / cores, the elements of a turn on the two outer bodies / cores of the same trapezoidal shape and rectangular on the inner bodies / cores of the same shape. They line up and contact each other along the outer edge of the two outer bodies / cores with the longer of the two parallel trapezoidal sides. In the respective gap between the two outer bodies / cores and the immediately adjacent core on the shorter side of the two mutually parallel trapezoidal sides of an element of the turn, a rectangular element of the turn is lined up with its equally long side and makes electrical contact. In the respective gap between the bodies / cores lying on the inside, there are rows and always contact two rectangular elements of the winding. Thus, the turns with the bodies / cores are in a tissue-like manner while maintaining the minimum necessary insulation spacing and there is a connection tab for the external connection at each end of a winding.

The I-Inductor is therefore suitable for high cut-off frequencies up to 10 GHz with sufficient quality Q <500. The RF permeability expediently lies in the direction of the magnetic field axis in the cores. The shielding currents are significantly reduced by the arrangement of the conductor elements and the body or layers of magnetic material. Since the design can be kept very compact, the parasitic capacitance is low.

The I inductor is explained in more detail below with reference to the drawing with FIGS. 1 to 8. Show it:

FIG. 1 shows the basic sketch of the I inductor,

FIG. 2 the tape winding for the I inductor,

3a shows the construction of double trapezoidal elements with two cores,

3b shows the structure of double trapezoidal and rectangular elements with more than two cores,

FIG. 4 the I-inductor with secondary windings as an HF transmitter,

FIG. 5 the I inductor in the gap of a C magnet,

FIG. 6 shows the inductance curve of the I inductor according to FIG. 3a.

The I-inductor which is now described in more detail is an HF microinductor with typical dimensions as indicated in FIG. 3a. It is a component for microsystem technology in planar technology and is used in facilities for high frequencies at 1 - 10 GHz. It is made using thin-film technology. The length of the I-inductor is limited so that the physics necessary for the application, i.e. the planned microwave technical property, is emphasized, namely the upper limit for the overall length in the x direction (see coordinate system in Figures 1 and 5)

α is a pure number factor; 0.1 was found to be optimal for technical application, c is the speed of light, f is the frequency and μ _{rx is} the relative magnetic permeability constant in the x-direction.

First of all, the principle will be presented with reference to FIG. 1: The I-inductor consists of two parallel, expediently rectangular bodies - also in magnetic terms: cores - made of a magnetically permeable material. A solenoid is wound on each iron core. Both solenoids can be electrically connected differently, once each connected separately, the other in series or in parallel, but in any case in such a way that the magnetic field in one core has the opposite direction to that in the other. Thus, when both solenoids are energized, there is a magnetic circuit, namely through the two cores and over the two gaps at the two end regions of the arrangement, the magnetic flux thus closes over the two gaps. The gap can be filled with the same magnetic material. When using magnetically anisotropic materials, preferably with an anisotropy that has the preferred direction from one core in the direction of the other. For high-frequency use, the gap should be as small as possible, or at least so small that there is still sufficient electrical insulation resistance for operation. The size of the entire arrangement is also limited by parsitary capacities.

The two solenoids are wound in Figure 2 from a winding and thus not separately. For the optimal quality of the I It is favorable for the inductor to integrate the upper and lower solenoids with one another. The sketched winding technique shows that one turn of the upper solenoid is always connected in series to one of the lower and vice versa until the entire winding is finished. The respective winding direction is such that the two magnetic fields generated add up in a circle and do not subtract or cancel. So there are not two separate solenoids in a row. This structure can be easily created with planar technology or layering technology by successively building up the layers. However, the respective conductor connections must be retrofitted in the gap and on the outer longitudinal edges.

The construction according to FIG. 3a is favorable in terms of production technology - also in terms of its high-frequency properties. The winding, in principle as in Figure 2, is constructed from double trapezoidal conductor elements made of copper or aluminum by stringing them together. One half of the double trapezoidal structure lies on the back of one body, the other half is pulled through the gap and placed on the other body. This is followed by the next double trapezoidal conductor element in the same manner until the double winding on the two bodies or cores is finished. With this special construction, the two windings consist of six double trapezoidal elements made of aluminum. A connecting lug is then attached to both ends for the electrical connection. The structure using parallelogram elements goes accordingly. Both cores are made of an iron alloy, in which the magnetic anisotropy can be adjusted by the manufacturing process.

For the more than two-core structure, the representation on the three-core arrangement according to FIG. 3b is sufficient. The dimensions in it are exemplary. The trapezoidal conductor elements lie behind as before on the two outer bodies / cores, the body / core lying in between has the rectangular conductor strips which are as wide on both sides as ^' the smaller of the two parallel trapezoidal sides and also connect along there. In contrast to the two outer bodies / cores, which are almost completely covered with the conductor elements over the winding width up to the winding spacing, the assignment with this technique is only for the intermediate body / core and thus for the intermediate body / core up to half the case. The rectangular conductor elements are lined up alternately behind and in front on an intermediate body / core along the same. In order to have the greatest possible coverage of the same by the conductor of the winding in the case of more than two bodies / cores across the winding width, each body / core must be wound with a conductor on its own and not simultaneously with one or the other.

FIG. 6 shows the course of the inductance of the I inductor in nH as a function of the permeability μ _rx present in the x direction, the windings of which are constructed from double trapezoidal elements according to FIG. 3a. The core or iron layers here have a contour of 320 x 40 x 2 (μm) ³ . The permeability μ _ry in the y direction is 1. With μ _rx = 1000, an inductance of 3 nH is achieved with this structure.

Before a concrete structure is completely presented, the structure of a high-frequency transformer or transformer based on the I-inductor principle should also be explained with reference to FIG. The main areas of application for this are telecommunications and there in assemblies such as blocking circuits or cell phones. But also in communications technology, such as satellite technology or in digital network technology for data long-distance transmission, dial-up, this technology finds its way because it is further miniaturized.

The principle of antiparallel magnetic excitation is used to build a high-frequency transmitter and thus the electrical isolation of circuits is achieved, or it is used to build a microtransformer (Figure 4). Both for an I-inductor (FIGS. 1 to 3) and for the high-frequency transmitter based on this principle, the frequency range is increased by applying an anisotropy. In the present case, this is achieved by an external, static and perpendicular magnetic field to the I inductor, which is generated, for example, by a planar H or C magnet (FIG. 4). The core of the planar H or C magnet is also made of the same material with uniaxial anisotropy for simplifying manufacturing reasons. By varying this static magnetic field, the cut-off frequency of the component is increased with increasing magnetic flux density, or the inductance is reduced. For reasons of installation or connection technology, the C-magnet should be the preferred component, less the H-magnet.

FIG. 5 shows a top view of the I inductor installed in the air gap of the C magnet. The implementation is carried out using planar technology. The dimensions given give an impression of the miniaturization potential. The I-inductor itself is constructed and wound according to Figure 2. It is only 60 - 70 μm wide and has a gap between the cores and the respective poles of around 4 μm. The free space in the C interior is approximately (250 μm) ² , corresponding to the outer contour of approximately 800 μm or 0.8 mm in length. The static field generation B _stat in the C magnet is extremely efficient, since magnetically uniaxial anisotropic materials have a permeability »1 in the y direction in the static case. The magnetic anisotropy in the C material expresses the permeability of μ _s tatχ 350 and μ _s taty «1000, for the I-inductor itself the relationships are as follows: μ _HF χ ∞ 350 and

The five winding packages on the C-yoke have direct current flowing through them and therefore generate a constant or static magnetic field that penetrates the HF field in the cores of the I-inductor vertically and thus increases the magnetic anisotropy and thus the cutoff frequency. Isotropic magnetic materials cannot be used for this application.

literature

I see "Ferromagnetism" by Kneller, E., pages 642 and 643, "Snoek'sche Limit" (page 643), Springer Verlag Berlin / Göttingen / Heidelberg, 1962

II

Shinji Tanabe, Yasuhiro Shiraki, Kenji Itoh, Masahiro Yamaguchi, Ken-ichi Arai, FEM Analysis of Thin Film Inductors Used in GHz Frequent Bands IEEE Transactions on Magnetics., Vol 35, No: 5, September 1999)

III

J. Driesen, W. Ruythooren, R. Belmans, J. De Boeck, J-P. Celis, K-Hameyer, Electric And Magnetic FEM Modeling Strategies For Micro-Inductors, IEEE Transactions on Magnetics. , Vol 35, No: 5, September 1999)

IV

A. Gromov, V. Korenivskim, K.V. Rao R. B. van Dover, P. M.

Mankiewich, A Model for Impedance of Planar RF Inductors Based on Magnetic Films, IEEE Transactions on Magnetics 1998)

Claims

Claims:

1. I-inductor as a high-frequency micro-inductor, HF inductor for short, for microsystem technology, consisting of at least two in a rectangular delimiting plane with a gap formation, band-shaped, with their respective longitudinal axis parallel to each other, of equal length and for the intended magnetic Flux through them necessarily thick bodies / cores made of magnetically permeable material, which are provided with at least one winding in such a way that when the winding is energized, the magnetic field generated by the winding in the associated body / core through the in the associated winding of the winding in the immediately adjacent body / Magnetic field generated core is strengthened and not weakened, for which purpose the magnetic flux runs completely or almost completely in the magnetic material of the body / core.

2. I-inductor according to claim 1, characterized in that the material of the body / cores is magnetically isotropic.

3. I-inductor according to claim 1, characterized in that the material of the body / cores is unidirectionally or uniaxially magnetically anisotropic.

4. I-inductor according to claims 2 and 3, characterized in that the two outer bodies / cores ^' ne the arrangement of the same width and the intermediate body / cores are at least as wide.

5. I-inductor according to claim 4, characterized in that the respective winding consists of one solenoid per body / core.

6. I-inductor according to claim 4, characterized in that the turns of a winding with the bodies / cores form a woven structure.

7. I-inductor according to claims 5 and 6, characterized in that the windings of the winding consist of a strip conductor which forms a connecting lug for the external connection at both ends.

8. I-inductor according to claim 6, characterized in that the elements of a turn of the winding consists of band-shaped square elements,

- which are similarly trapezoidal in the case of only two bodies / cores lying next to each other, two trapezoidal elements in the gap between the two bodies / cores with the shorter of the two parallel trapezoid sides and along the outer longitudinal edge of the two bodies / cores with the longer one line up the two parallel trapezoidal sides and make electrical contact,

- In the case of more than two adjacent bodies / cores, the elements of a turn on the two outer bodies / cores are of a similar trapezoidal shape and rectangular on the inner bodies / cores are similar, the trapezoidal elements of the turn along the respective outer edge of the Line up the two outer bodies / cores with the longer of the two parallel trapezoidal sides and make electrical contact, in the respective gap between the two outer bodies pern / cores and the immediately adjacent core on the shorter side of the two mutually parallel trapezoidal sides of an element of the turn a rectangular element of the turn with its equally long side and electrically contacted, and in the respective gap between the inner bodies / cores Always line up two rectangular elements of the turn and make electrical contact so that the turns with the bodies / cores are in a tissue-like manner while maintaining the minimum necessary insulation spacing and there is a connection lug for the external connection at each end of a winding.