WO2002006844A1

WO2002006844A1 - Assembly for transmitting signals using magnetoresistive sensor elements

Info

Publication number: WO2002006844A1
Application number: PCT/DE2001/002476
Authority: WO
Inventors: Wolfgang Clemens; Michael Vieth
Original assignee: Siemens Aktiengesellschaft
Priority date: 2000-07-17
Filing date: 2001-07-04
Publication date: 2002-01-24
Also published as: DE10034732A1

Abstract

The signal transmission assembly has an electric conductor strip (11) that generates a magnetic signal field by means of a current flow (I), in addition to several magnetoresistive sensor elements (7i) with a magnetization (mi) that are connected using two bridge branches (Z1, Z2) to form a complete or partial bridge (B). The conductor strip (11) is guided over the sensor elements (7i) in such a way that alternately a sensor element from the first bridge branch (Z1) and from the second bridge branch (Z2) is detected by said strip (11) and the same current flow direction (I) is given in diagonal sensor elements (71, 74 or 72, 73).

Description

description

Arrangement for signal transmission using magnetoresistive sensor elements

The invention relates to an arrangement for signal transmission with at least one electrical conductor track that generates a magnetic signal field by means of current flow, as well as a plurality of magnetoresistive sensor elements that are connected to the conductor track and are galvanically separated from it, which are connected to a full or partial bridge with two bridge branches.

In many areas of technology such as digital information transmission or measurement technology requires a floating transmission of electrical signals. So-called optocouplers are mainly used for galvanically isolated signal transmission in communication and automation technology. Here, an electrical (primary) data signal is given to an input, which is converted into an optical radiation signal by means of a light-emitting diode (LED). This radiation signal is transmitted through an insulating, optically transparent medium to an optical sensor or detector element, where it is converted back into an electrical (secondary) signal.

Such a digital information transmission by means of optocouplers is limited in the transmission rate by the limited bandwidth of the optical elements (with approximately 50 MBd corresponding to 25 MHz) and in the design by the limited integrability of the optical elements with silicon technology. Furthermore, the optical elements can only be operated in a temperature range up to a maximum of about 85 ° C. and moreover generally only with operating voltages of at least 5 V. In addition to such an optoelectric signal transmission, magnetic transmission using Hall probes, for example, is also known. Such probes can be used to record all of the signal quantities that generate or influence magnetic fields. For example, a corresponding, potential-free measurement of a current can be found in the book by E. Schrüfer "Electrical Measurement Technology", 6th edition, 1995, Hanser-Verlag Munich, pages 165 to 168.

In the field of magnetoelectronics, it is also possible to use magnetoresistive sensor elements to set up so-called magnet couplers, which also enable galvanically isolated data transmission. Here the indicated limits of the optocouplers can be significantly exceeded, e.g. with a significantly higher data transfer rate and the possibility of operating corresponding components even at voltages lower than 5 V. Such magnetic couplers are also to be integrated with electronic components of Si technology. Of course, they can also be used for analog current measurement after appropriate adjustment.

A corresponding magnetic coupler was proposed with the unpublished DE patent application 100 17 374.8 from 7.4.2000. According to a special embodiment, it contains several magnetoresistive sensor elements connected to form a full or partial bridge with two bridge branches. At least one electrical conductor track generating a magnetic signal field by means of current flow is assigned to these sensor elements. Each sensor element comprises a multilayer system showing an increased magnetoresistive effect, which contains at least one soft magnetic measuring layer, at least one further ferromagnetic layer and at least one non-magnetic intermediate layer arranged in between, the magnetization of the soft magnetic measuring layer seeing one of the preferred axes of the magnetization in the absence of a signal field has a predetermined starting position dependent on this layer. The preferred axis of magnetization is sensor-intrinsic; That is, their imprinting can take place not only through a special layer structure, for example through selection of the material and / or the layer thickness, but also through a certain geometric shape, for example through a predetermined ratio of length to width, and / or through an embossed by an external magnetic field Anisotropy happen. Such anisotropy can be generated either during the manufacturing process or afterwards by a tempering step in a magnetic field. Corresponding magnetocouplers can be operated up to around 150 ° C and can be integrated or combined with components from silicon technology.

The multilayer systems of the magnetocoupler can also be designed as magnetoresistive tunnel elements, their non-magnetic intermediate layers then consisting of an electrically insulating material.

WO 98/07165 also shows a magnetocoupler which has four sensor elements for current detection, with which a magnetic signal field is to be detected, which is generated by means of current flow 'through a flat coil. The conductor tracks of this flat coil thus extend orthogonally through the ^'sensor elements and are electrically against these separately. Here, too, the sensor elements are each constructed as multi-layer systems with two ferromagnetic layers, which are each separated by an electrically conductive, non-magnetic intermediate layer and are magnetoresistive, anisotropic. The multilayer systems can in particular show the so-called GMR effect.

The object of the present invention is now to design the arrangement for signal transmission with the features mentioned at the outset in such a way that it enables a particularly simple construction of its magnetoresistive sensor elements. This object is achieved according to the invention in that, in the absence of a signal field, each magnetoresistive sensor element has magnetization with a starting position pointing in the same direction and the conductor track is guided from the two bridge branches via sensor elements such that an alternating sensor element from the first Bridge branch and a sensor element arranged diagonally in the bridge from the second bridge branch is detected and the same current flow direction is given in diagonal sensor elements.

The magnetoresistive sensor elements can be anisotropically magnetoresistive (so-called "AMR elements"), giant magnetoresistive (so-called "GMR elements"), tunneling magnetoresistive (so-called "TMR elements") or colossal magnetoresistive (so-called "CMR elements") ) (see, for example, the volume "XMR Technologies" (Technology Analysis: Magnetism, Volume 2)) of the VDI Technology Center "Physical Technologies", Düsseldorf (DE) 1997, pages 11 to 46). The current path of the signal transmission is separated by at least one insulation layer over the bridge arrangement of these elements in such a way that signals of different signs are contained on the individual sensor elements and a bridge arrangement is thus provided. Such a bridge arrangement advantageously shows an extensive one

Temperature stability of the signal, since the resistances of the individual sensors change in the same way with temperature fluctuations. It is irrelevant whether a full bridge or a partial bridge such as e.g. builds a half-bridge (cf. DE 195 07 303 AI or

DE 196 19 806 AI). The structure of the bridge arrangement makes it possible to ensure that the sensor elements which have a preferred direction can be magnetized in the same direction and nevertheless changes in resistance with different signs are measured on the individual sensor elements. The advantages of the measures according to the invention can thus be seen in the fact that a simple structure of the signal transmission Support arrangement with its magnetocouplers connected to a full or partial bridge is made possible due to the uniform magnetizations of the sensor elements.

Advantageous refinements of the signal transmission arrangement according to the invention emerge from the dependent claims.

For example, according to a special embodiment, each of their sensor elements can comprise a multilayer system which exhibits an increased magnetoresistive effect and contains at least one soft magnetic measuring layer, at least one further ferromagnetic layer and at least one non-magnetic intermediate layer arranged between them. These multilayer systems can form particularly sensitive gantant-magnetoresistive or tunnel-magnetoresistive sensor elements with a hard and a soft magnetic part. The hard magnetic sensor part advantageously needs to be magnetized only once in production, so that the magnetization direction is permanently maintained. The soft magnetic layer can now be easily aligned using an external magnetic field. The electrical resistance of the sensor elements depends on the relative position of the magnetization of the hard and soft magnetic layers. In this case, temperature influences are advantageously reduced in that a bridge arrangement is provided here, sensor elements which are premagnetized antiparallel are connected to one another.

The current track can be used for magnetization in a particularly simple manner in order to magnetize and thus align the hard magnetic layers of the sensor elements by means of a correspondingly large current surge.

The signal transmission arrangement according to the invention preferably has means for its magnetic shielding against external magnetic interference fields. Appropriate means can in particular on the side of the at least one conductor track facing away from the sensor elements and optionally galvanically separated from it in the form of a soft magnetic layer. Such a layer can advantageously also perform the function of a magnetic mirror with respect to the magnetic field signal caused by the at least one conductor track and can thus contribute to a corresponding signal amplification.

Of course, the signal transmission arrangement according to the invention can advantageously be used as a current sensor. A current flowing through their electrical conductor track can namely be generated to generate a primary signal field, which is then detected by the magnetoresistive sensor elements and converted into a secondary signal.

It is also advantageous that the signal transmission arrangement according to the invention can be integrated with components of silicon technology.

Further advantageous refinements of the signal transmission device according to the invention emerge from the remaining subclaims.

To further explain the invention, reference is made below to the drawing, in the figures of which each schematically illustrates parts of power transmission devices according to the invention. 1 shows a hard-soft structure of a magnetoresistive sensor element, FIG. 2 shows characteristic curves of various suitable sensor elements, FIG. 3 shows a bridge formwork according to the prior art, FIG. 4 shows characteristic curves that result from the bridge circuit according to FIG. 3, Figure 5 shows a cross section through a layer structure of a

6 a bridge structure of a signal transmission arrangement according to the invention, FIG. 7 a cross section through the bridge structure according to FIG. 6, FIG. 8 a suitable bridge structure in the form of a half bridge and FIG. 9 a suitable magnetic shielding against external stray fields. Corresponding parts are provided with the same reference symbols in the figures.

Giant magnetoresistive (GMR) or tunnel magnetoresistive (TMR) sensor elements in the so-called spin valve structure are advantageously used for the signal transmission arrangement according to the invention. A corresponding basic structure of a corresponding sensor element with hard and soft magnetic layers can be seen from the sectional view in FIG. 1. 1 denotes a hard magnetic layer, 2 a magnetization direction of this layer, 3 a non-magnetic intermediate layer, 4 a soft magnetic layer, 5 a magnetization direction of this soft magnetic layer and 6 an external magnetic field H _ex . The hard magnetic layer 1 of the sensor element, generally designated 7, can be a single layer, for example made of Co or a Co alloy, or can also consist of a layer system. Such a layer system can in particular be designed as a so-called artificial antiferromagnet AAF (artificial antiferromagnet) (cf. WO 94/15223), which behaves like a permanent magnet and can also be regarded as a bias layer part. Instead, the layer system can also form a natural antiferromagnet NAF with a magnetic layer coupled to it. A combination of both types of layer system is of course also possible. Also a fari- agnet with a coupled magnetic layer is conceivable instead of the NAF system. The non-magnetic intermediate layer 3 can be a metallic layer in the case of a GMR sensor element. Instead, in the case of a TMR sensor element, it can also consist of an insulating material or a semiconducting material. The soft magnetic layer 4 is only weakly magnetically coupled to the hard magnetic layer 1 or a corresponding layer system or is decoupled from this layer / layer system. Anisotropy may or may not be impressed on the soft magnetic layer. There are different characteristics. Both variants can be used for the sensor elements. The structure shown can of course also be repeated several times in a layer system in order to increase the sensor effect (cf. the aforementioned WO 94/15223 A).

FIG. 2 shows typical characteristics of individual sensor elements of the spin valve type with and without anisotropy. The upper diagram a) shows the characteristic (resistance R as a function of the field strength of the external field H _ex ) for an uncoupled spin valve system. A hysteresis of the characteristic curve is shown with a remanent magnetization without an external field. The characteristic curve shown in diagram b) below results for an uncoupled spin valve system, the soft magnetic layer (measuring layer) having an impressed anisotropy. Such anisotropy can be generated in a manner known per se by a variety of measures. The characteristic curve is shown in the event that this anisotropy is oriented perpendicular to the magnetization of the hard magnetic layer. Other orientations are of course also possible.

In a known manner, other methods are also possible for applying a preferred direction in the soft magnetic layer, for example by means of an external field or by a slight coupling to the hard magnetic layer. 3 shows a known Wheatstone bridge arrangement of sensor elements 7ι. Four sensor elements 7i (with i = 1 .... 4) are connected together in two bridge branches ZI and Z2, the sensor elements belonging to a bridge branch having an antiparallel orientation of the hard magnetic layer to one another. The corresponding magnetization directions of the sensor elements 7ι are im (with i = 1 .... 4). Of course, a so-called half-bridge construction or partial bridge construction is also possible (cf. DE 196 19 806 AI mentioned). In the figure, there is also a basic electrical potential with GND, with U a higher voltage potential, on which the two bridge branches Zl and Z2 are placed, and with VI and V2 the voltage potentials at the corresponding taps for the bridge voltage V = V1-V2 designated.

4 shows typical characteristic curves for a bridge arrangement of the sensor elements according to FIG. 3, specifically for the case of the characteristic curves of the individual elements according to FIG. 2: a) = without anisotropy of the soft magnetic layer, b) = with anisotropy of the soft magnetic layer. Ideally, there is no longer an offset.

FIG. 5 shows a cross section through a structured integrated layer structure for a current sensor or a magnetocoupler 9 from a bridge circuit of a signal transmission arrangement according to the invention. Representing the magnetoresistive sensor elements of this arrangement, only a single sensor element 7ι is shown here as an entire layer package. The sensor elements are advantageous by

Sputtering applied to a substrate 8, for example a thermally insulated Si wafer. The individual sensor elements are produced by structuring steps. There is at least one passivation layer 10 in order to protect the sensor element in particular from environmental influences. This passivation layer also serves as an insulation layer. A combination of passivation and isolation Layer. The required current conductor tracks 11 are applied thereon, which are structured as illustrated, for example, in FIGS. 6 and 8 below. A current I is sent through the current conductor tracks, the direction of current flow of which is illustrated with the character that is usually used. The desired information is to be transmitted by means of this stream. A magnetic field 12 forms around the current conductor tracks and is now detected by the sensor elements 1. This enables galvanically isolated signal transmission. It now depends on the layer system used and the subsequent evaluation electronics whether the signal is transmitted analog or digital. In the first case there is an analog current sensor, in the second case, for example, a magnetocoupler.

FIG. 6 shows an exemplary embodiment of an advantageous course of the path for a current I over a conductor track 11 for a signal transmission arrangement according to the invention in supervision. The sensor elements 7χ to 7 are connected to form a bridge arrangement B. They can advantageously be formed on a common level of a substrate. However, in contrast to the embodiment according to FIG. 3, the hard magnetic layer is magnetized in the same direction in all sensor elements. The magnetizations m_, l to m4 therefore all point in the same direction. This is a great advantage because the entire wafer can be magnetized homogeneously during production. In addition, layer structures can be used, such as exchange bias systems, in which the magnetization has to be carried out in a relatively complex manner, for example with a specific temperature cycle. Here, the current path 11 is guided over the individual sensor elements such that elements adjacent to one another within a current branch ZI or Z2 and sensor elements in the two current branches see an antiparallel magnetic field. That is, each magnetoresistive sensor element 7j. If there is no signal field, the current track has magnetization with a starting position pointing in the same direction. The line should terbahn 11 be guided over the sensor elements from the two bridge branches ZI and Z2 in such a way that a sensor element from the first bridge branch ZI and from the second bridge branch Z2 is detected alternately and thus the same current flow direction is given in diagonal sensor elements of the bridge order B. Consequently, the direction of current flow across the sensor element pairs <lχ-li and 7 ₂ -7 ₃ is the same in each case. Then a bridge signal as shown in FIG. 4 can also be advantageously achieved by the respective characteristic curves. The structure shown is much simpler than other alternatives, such as are known, for example, as compensation circuits for current sensors. Of course, other embodiments than the structure shown in FIG. Β are also possible; it is only important that the current conductor track 11 is guided over the individual sensor elements 7i in such a way that, seen from the electrical side, a bridge arrangement is created which enables a differential measurement.

FIG. 7 shows a cross section through the layer structure for a magnetocoupler with a bridge arrangement according to FIG. 6 in a representation corresponding to FIG. 5. As can be seen from the figure, the magnetic field 12 of two adjacent parts of the current conductor path 11 through which the same current I flows, but in the opposite direction, is antiparallel to one another. The characteristics of the underlying sensor elements 7 are thus reflected, resulting in a bridge signal.

FIG. 8 shows the design of the current path through a current conductor track 11 for a half-bridge structure, a representation corresponding to FIG. 6 being chosen. It may be the case that with certain sensor structures, full-bridge switching is not possible or can only be implemented with great effort. A half-bridge arrangement as shown in FIG. 8 is also suitable here. In this case, only two sensor elements, such as elements 7 ₂ and 7 ₃ , lie below the current conductor path 11, while the others are not influenced by their signal field become. The two unaffected sensor elements 7χ and 7 ₄ can optionally be replaced by normal resistors (see, for example, the aforementioned DE 195 07 303 AI); with respect to a temperature stability of the signal, it is however advantageous lχ also for the elements and to choose 7 ₄ sensor structures as for the other sensor elements 7 ₂ and 7. ₃

In addition, according to the cross section shown in FIG. 9, a soft magnetic layer 15 or a soft magnetic layer structure can be built into the structure, which reduces / shields the influence of external stray fields. This is generally advantageous since the sensor elements 7_. must be designed very sensitive for effective data transmission. Such a soft-magnetic layer structure or the soft-magnetic shielding layer 15 can also be used to more effectively couple the magnetic field of the current track to the assigned sensor elements or to increase the field strength at the sensor elements. The soft magnetic layer or layer structure can also be shaped in a certain way in order either to achieve better shielding of the external stray fields H _st or to achieve a better coupling of the field generated by the electrical conductor 11. The soft magnetic shielding layer must of course be electrically insulated from the individual turns of the electrical conductor 11. An insulation layer 14 shown in the figure is used for this.

Claims

claims

1. Arrangement for signal transmission with at least one electrical conductor track generating a magnetic signal field by means of current flow ^λ and several to a full or

Partial bridge with two bridge branches interconnected, assigned to the conductor track and galvanically separated from it, magnetoresistive sensor elements, characterized in that, in the absence of a signal field (12), each magnetoresistive sensor element (7ι) has magnetization (im) with a starting position pointing in the same direction and the conductor track ( 11) is guided over the sensor elements (7- from the two bridge branches (ZI, Z2) such that a sensor element from the first bridge branch (ZI) and from the second bridge branch (Z2) is alternately detected by it (11) and the same current flow direction is given in diagonal sensor elements (lχ, 7 or 7 ₂ , 7 ₃ ).

2. Arrangement according to claim 1, characterized in that the sensor elements (7) each comprise a multilayer system showing an increased magnetoresistive effect, the at least one soft magnetic layer (4), at least one further ferromagnetic layer (1) and at least one arranged in between , contains non-magnetic intermediate layer (3).

3. Arrangement according to claim 1 or 2, provided by a multilayer system with a magnet layer (1) which is magnetically harder than the at least one soft magnetic layer (4) and spaced apart by the non-magnetic intermediate layer (3) or a corresponding layer system.

4. Arrangement according to claim 3, d a d u r c h g e - k e n n z e i c h n e t that the magnetically harder

Layer system as a multilayer artificial antiferromagnet (AAF) and / or a natural antiferromagnet (NAF) or a ferrimagnet with a coupled magnetic layer is formed.

5. Arrangement according to one of claims 2 to 4, so that the multilayer system is designed as a magnetoresistive tunnel element with an insulating or semiconducting intermediate layer (3).

6. Arrangement according to one of the preceding claims, at least largely by designing the sensor elements (7ι) at least largely on a common plane of a substrate (8).

7. Arrangement according to one of the preceding claims, characterized by means for its magnetic shielding against external magnetic interference fields (H _sc ).

8. Arrangement according to claim 7, d a d u r c h g e k e n n - z e i c h n e t that at least one soft magnetic

Layer (15) is arranged as a shielding means on the side of the at least one conductor track (11) facing away from the sensor elements (7i) and insulated from it.

9. Arrangement according to one of the preceding claims, g e k e n n z e i c h n e t by use as a current sensor or a magnetocoupler.

10. Arrangement according to one of the preceding claims, g e - k e n n z e i c h n e t by integration with components of silicon technology.