WO1996038739A1

WO1996038739A1 - Magnetic field sensor with a bridge arrangement of magneto-resistive bridging elements

Info

Publication number: WO1996038739A1
Application number: PCT/DE1996/000960
Authority: WO
Inventors: Wolfgang Schelter; Hugo Van Den Berg
Original assignee: Siemens Aktiengesellschaft
Priority date: 1995-06-01
Filing date: 1996-05-31
Publication date: 1996-12-05
Also published as: DE19520206A1; EP0874999A1; KR19990022160A; DE19520206C2; JPH11505966A

Abstract

The invention concerns a sensor with a bridge arrangement (B1) of a plurality of magneto-resistive thin film bridge elements (E1 to E4). All the bridge elements (E1 to E4) are constructed with the same layered structure on a common substrate (13) and display a giant magneto-resistive (GMR) effect. In addition, each bridge element has a bias layer part and a conductive layer (6i) which is provided for guiding a set current (Ie) in order to set in a fixed manner a given orientation direction for the magnetization in the bias layer part.

Description

description

Magnetic field sensor with a bridge circuit of magnetoresistive bridge elements

The invention relates to a sensor for detecting an external, at least largely homogeneous magnetic field with magnetoresistive bridge elements with a thin layer structure connected to form a bridge, via which bridge a bridge current is to be conducted and from which a measuring voltage is to be taken. Such a sensor is indicated in DE-GBM 93 12 674.3.

In ferromagnetic transition metals such as Ni, Fe or Co and their alloys, the electrical resistance can depend on the size and direction of a magnetic field penetrating the material. The corresponding effect is called anisotropic magnetoresistance "AMR" or anisotropic magnetoresistive effect. Physically, it is based on the different scattering cross sections of electrons with the spin polarity of the D band and different spin. The electrons are therefore referred to as majority or minority electrons. For corresponding magnetoresistive sensors, a thin layer of such a magnetoresistive material with a magnetization in the layer plane is generally provided. The change in resistance when the magnetization rotates with respect to the current direction can be a few percent of the normal isotropic (= ohmic) resistance (cf. the DE-GBM mentioned at the beginning).

Furthermore, magnetoresistive multilayer systems have been known for some time, which contain a plurality of ferromagnetic layers arranged in a stack, which are separated from one another by metallic intermediate layers and the magnetizations of which lie in the layer plane. The thicknesses of the individual layers are significantly smaller than that average free path length of the line electrons selected. In such multilayer systems, in addition to the mentioned anisotropic magnetoresistive effect AMR, a so-called giant magnetoresistive effect or giant magnetoresistance GMR can occur in the individual layers (cf. for example EP-A-0 483 373). Such a GMR effect is based on the differently strong scattering of majority and minority conduction electrons at the interfaces between the ferromagnetic layers and the intermediate layers as well as on scattering effects within the layers, especially when alloys are used. The GMR effect is an isotropic effect. It can be considerably larger than the anisotropic effect AMR and can assume values of up to 70% of the normal isotropic resistance. In the multilayer systems which show a GMR effect, adjacent metallic magnetic layers are initially magnetized in opposite directions. Under the influence of an external magnetic field, the initial anti-parallel alignment of the magnetizations can be converted into a parallel one. This fact is exploited with corresponding magnetic field sensors.

From the DE-GBM mentioned at the outset, a magnetic field sensor emerges with whose bridge elements (sensor elements), which show an anisotropic magnetoresistance AMR, a Wheatstone bridge circuit can be constructed. The fact that the magnetoresistive effect of their AMR layers in the individual sensor elements in the individual sensor elements depends on the angle between the magnetization of the respective layer and the direction of a current flowing through it can be exploited in a targeted manner in the bridge circuit of such a sensor . The individual sensor elements can advantageously be connected to the bridge by appropriate structuring so that the current directions in the two pairs of diagonal bridge elements from the two bridge branches are opposite. The object of the present invention is to design the magnetic field sensor with the features mentioned at the outset in such a way that it can be used to measure one or more vector components of a magnetic field which is at least largely homogeneous (= uniform) in the receiving range of the sensor, with high sensitivity, wherein a measurement signal is obtained which is at least partially compensated for in terms of temperature influences and mechanical stresses in the bridge elements. In addition, the sensor should be relatively easy to manufacture.

This object is achieved in that all bridge elements are formed on a common substrate with the same layer structure and the same geometry and show an increased magnetoresistive effect (GMR) and that a bias layer part and a conductor layer are provided in each of the bridge elements, this conductor layer for guidance a setting current of a predetermined direction and strength is provided such that an orientation direction of its magnetization can be permanently set in the bias layer part.

The advantages associated with this configuration of the magnetic field sensor can be seen, in particular, in the fact that for the first time a possibility has been created for large-scale use with reasonable expense to design GMR bridge elements with the same structure in a bridge circuit of extremely small dimensions. This is because, by means of the setting current through the conductor layers respectively assigned to the individual bridge elements, predetermined orientation directions of the magnetizations in the respective bias layer parts of the individual bridge elements can be "fixed" in a simple manner. That is, the bias layer part which is magnetically harder than other magnetic layers of a bridge element and which consists both of a single magnetically harder layer or of a layer system. stem, which can be regarded in particular as an artificial antiferromagnet (cf. DE 42 43 358 A), is advantageously magnetized one-time by means of the magnetic field caused by the adjusting current. The set current is to be chosen so high that it can be used to obtain a magnetic field which is sufficiently strong for the magnetic reversal of the bias layer part. The magnetic field of the set current can optionally be overlaid by an external support or auxiliary field. In contrast, due to the predetermined magnetic hardness (coercive field strength) of the bias layer part, the external magnetic field component to be detected is not able to reverse magnetize the bias layer part.

With the bridge circuit of these bridge elements, it is also possible, depending on the external magnetic field component, to obtain an at least largely temperature-compensated and mechanical stress-compensated measurement signal. This is made possible by the same layer structure of the individual bridge elements side by side on the common one

Substrate reached. A layer structure is understood to mean that each bridge element has a predetermined layer sequence with a predetermined thickness of the individual layers. The layer sequences and the thicknesses of corresponding layers from all bridge elements are the same. Such layer sequences can advantageously be easily realized.

Advantageous refinements of the magnetic field sensor according to the invention emerge from the claims subordinate to the main claim.

To further explain the invention, reference is made below to the drawing. Each show schematic 1 shows the circuit diagram of a bridge circuit of a magnetic field sensor according to the invention, FIG. 2 shows an oblique view of a GMR layer structure of an individual bridge element of such a sensor, FIG. 3 shows a cross section through a bridge element according to the invention, FIGS. 4 and 5 are views of bridge circuits of magnetic field sensors according to the invention, a plan view of a plurality of magnetic field sensors according to FIG. 4 and FIG. 7 the hysteresis curve of a bias layer part of a

Bridge element. In the figures, corresponding parts are provided with the same reference symbols.

A bridge circuit known per se is advantageously provided for the magnetic field sensor according to the invention, which is shown in FIG. 1. The bridge B shown contains two bridge branches ZI and Z2, which are connected in parallel between two connection points AI and A2 of the bridge. A bridge current Ig is to be conducted over the bridge B at the connection points AI and A2. Each of the bridge branches ZI and Z2 contains two bridge elements E1 and E2 or E3 and E4 connected in series. A measuring point P1 or P2 of the bridge lies between the two elements of each bridge branch. A measuring voltage U _{m can be} taken at these measuring points.

The individual bridge elements Ej (with 1 <j 4 4) of the bridge circuit B are to be built up from multi-layer systems known per se which have a GMR effect (cf. for example EP-A-0 483 373 or DE -OSen 42 32 244, 42 43 357 or 42 43 358). These multilayer systems each have, among other things, a bias layer part with a predetermined orientation direction of the magnetization m _fj . In Figure 1, these magnetizations are indicated by arrowed lines on the individual bridge elements illustrated. As can be seen from the figure, the two pairs E1-E4 and E2-E3 of diagonal bridge elements each have the same directions of the bias magnetizations mfj, the direction of magnetization of one pair being opposite to that of the other pair.

The bias field caused by the bias layers of each bridge element Ej is denoted by H ^ j. An external magnetic field to be measured, which is at least largely homogeneous (= uniform) in the detection range of the bridge circuit B, or a corresponding magnetic field component is illustrated by a double arrow denoted by H _m .

FIG. 2 shows the basic structure of a known multilayer system S with a GMR effect (cf. e.g. EP 0 346 817 A). This multilayer system contains a bias layer part 2, which according to the exemplary embodiment shown consists of a ferromagnetic bias layer 2a (e.g. made of NiFe) with an additional antiferromagnetic layer 2b underneath

(e.g. from FeMn). A measuring layer 3 which is magnetically softer than this bias layer part 2 (e.g. made of a NiFe alloy with a correspondingly smaller coercive field thickness) is separated by a non-magnetic intermediate layer 4 (e.g. made of Cu). The figure shows the possible magnetizations in these layers by means of arrowed lines. Corresponding multilayer systems are also referred to as "exchange biased systems".

Such or another multilayer system with a GMR effect can be, for example, the basic system for forming a bridge element Ej according to the invention. The bridge elements Ej preferably each have a multiplicity of magnetic and non-magnetic layers. Such a multilayer system is assumed for the bridge element Ej, which is indicated in FIG. 3. His multilayer system S ', which, for example, comprises a bias layer part 2 with several layers, is covered with a passivation layer 5, which consists of a non-magnetic and in particular insulating material. A conductor layer 6 in the form of a metallization made of a non-magnetic, electrically highly conductive material such as Cu or Ag is applied to this passivation layer 5. With a setting current I _e through this conductor layer 6, a magnetic setting field H _{e of} such a direction and strength can be caused that a preferred direction of the magnetization can be fixed in the bias layer part 2 of the multilayer system S '.

In FIGS. 4 and 5, corresponding strip-shaped conductor layers 6i (with 1 <i <3 and 1 <i <4) are for two

Arrangement options for four GMR bridge elements Ej in bridge circuits B1 and B2 of magnetic field sensors 11 and 12 according to the invention on a respective common substrate 13 are indicated. The bridge circuit B1 according to FIG. 4 has a rectangular arrangement of its bridge elements E1 to E4, while in the bridge circuit B2 according to FIG. 5 all four bridge elements E1 to E4 are arranged next to one another. The embodiment according to FIG. 5 advantageously allows a particularly narrow arrangement of the bridge elements. Three tracks of conductor layers 6i are required for the bridge circuit B1 and four tracks of conductor layers 6i are required for the bridge circuit B2. The directions of the individual setting currents I _e through the respective conductor layers to be selected, for example, are indicated by arrowed lines.

To connect the individual bridge elements to a bridge circuit B1 or B2 according to FIGS. 4 and 5, each element is provided with its GMR layer system with at least two contacts. These contacts are either both on the top measuring layer of the corresponding magnetic field sensitive layer system arranged so that the bridge current flows parallel to the layer planes on average (so-called "current-in-plane (CIP) system"); or a contact is arranged on the top and on the bottom layer, so that the bridge current then flows on average perpendicular to the layer planes (so-called "current-perpendicular-to-plane (CPP) system").

In general, the layer structure selected in each case is then coated with the passivation layer 5 according to FIG. 3 before the conductor layers 6i are applied to magnetize the individual bias layer parts.

To economically manufacture magnetic field sensors according to the invention, a large number of individual sensors are advantageously produced simultaneously on a common substrate, for example a silicon wafer. FIG. 6 shows a corresponding exemplary embodiment with 20 magnetic field sensors according to the invention on a disk-shaped Si substrate 13. Embodiments 11 according to FIG. 4 are used as a basis for these magnetic field sensors. Their respective bridge circuit B1 is only indicated by a flat rectangle in the figure. The interconnection of the conductor layers 6i of all bridge circuits leads to a meandering conductor track 16 between contacting surfaces 17a and 17b.

Of course, with the magnetic field sensors 12 according to the invention indicated in FIG. 5, a corresponding system of magnetic field sensors can be jointly formed on a substrate 13.

Corresponding systems of magnetic field sensors according to the invention can be implemented particularly easily with GMR bridge elements which are of the type of an exchange biased multilayer system S illustrated in FIG. 2. With such a system, the rigid magnet tization in the bias layer part 2 only small fields such as under 20 Oe are necessary. For example, with a conductor track 16 of 20 μm strip width and with a current of approximately 20 A, the required value of 20 Oe can be produced in the bias layer part.

With such a structure of a layer system, increased temperature conditions can advantageously be set during the magnetization of the bias layer part. For the FeMn layer of the layer system according to FIG. 2, for example, a temperature increase to approximately 150 ° C. is favorable. A corresponding temperature increase can take place, for example, by arranging the layer system in a heated room. If necessary, however, it is also possible to provide the heating power by means of the conductor layer 6i generating the magnetic adjustment field H _e . This can be done by selecting the appropriate conductor parameters (such as material, cross-section, electrical current I _e ).

If other multi-layer systems are provided, in particular with hard magnetic layers or with bias layer parts designed as artificial antiferromas, significantly higher, possibly up to 100 times higher, setting currents I _e may be required. There is then a risk that the heat losses that occur can destroy the GMR multilayer systems. In order to lower the relatively high current required, an additional external supporting field of strength H _z is advantageously added. This supporting field H _z is generated by external magnetic field sources such as magnetic coils or permanent magnets, the field direction of which with respect to the individual bridge elements must be adjustable (in particular reversible). The support field H _z and the setting field H _e on which this is based then make it necessary to exceed a predetermined threshold value of the field strength which, according to the assumed embodiment, the saturation field strength H _{s of} the bias layer part. The field relationships can be seen from the diagram in FIG. In this diagram, the field strength H is plotted in arbitrary units in the direction of the abscissa and the magnetization M in the direction of the ordinate. For the hysteresis curve shown, the quantities H _{s represent} the saturation field strength or the threshold field strength, H _c the coercive field strength and ^H min the field strength at which the magnetization M begins to increase sharply with increasing field strength from the value of the negative saturation magnetization. The size is ΔH = H _s - H _m -j_ _n = 2 * (H _s - H _z) .

In the case of a layer system with a so-called artificial antiferromagnet (cf. DE 42 43 358 A) it is necessary to exceed a threshold value, which need not be the saturation field strength H _s .

If one now exposes a multilayer system and in particular its bias layer part to an external additional field H _z which is directed parallel or antiparallel to H _e , the total field strength Hg on the multilayer system is added

Hg ⁼ ^ z + H _e .

For the field H _z , the size is preferably approximately

(H _s + H _{m; Ln} ) / 2 selected, H _e is selected slightly larger than ΔH / 2. An overall field then results at the bridge elements E1 and E4 (according to FIG. 1)

H _g = + | H _Z | + IH _e l,

while corresponding for the bridge elements E2 and E3

H Hg _g == ++ | H ₂ - IH. results If H _z and I _{e are selected} accordingly, the threshold value H is exceeded for the bias layer part of the bridge elements El and E4. This leads to a desired permanent orientation of the magnetization in this bias layer part. In contrast, the bridge elements E2 and E3, no change is effected for the bias layer part as H _m i _n is not exceeded. The magnetization of this layer part thus remains unaffected. If one now reverses the direction of H _z , the bridge elements El and E4 result in H _g = - | H _Z I + | H _e |, for E2 and E3 accordingly H _g = - | H _z | - | H _e I.

In this case, the threshold value H _{s is} exceeded for the bias layer part of the bridge elements E2 and E3, which leads to a desired permanent orientation of the magnetization in this bias layer part, while for the bias layer part of the bridge elements E1 and E4 the coercive field strength is not exceeded and the magnetization of this layer part remains unaffected, ie due to the previous process step in the opposite orientation.

According to the exemplary embodiment on which the diagram in FIG. 5 is based, it was assumed that an external magnetic support field of such a field strength H _{z is} selected that it alone cannot exceed the threshold field strength H _s . Of course, it is also possible to provide a correspondingly high supporting field and, if necessary, to generate an opposing field of such strength H _e with the setting field of the setting currents I _e that the threshold field strength H _{s may} not be reached in individual bridge elements.

It can thus be determined that with a corresponding design of a magnetic field sensor according to the invention on a substrate two types of magnetization rotated by 180 ° allow parts of the layer to be reached. In this way, a bridge circuit with GMR bridge elements can be constructed.

Claims

claims

1. Sensor for detecting an external, at least largely homogeneous magnetic field with magnetoresistive bridge elements with a thin-layer structure connected to form a bridge, via which bridge a bridge current is to be conducted and from which a measuring voltage is to be taken, that is, because of which,

- That all bridge elements (E1 to E4; Ej) are formed on a common substrate (13) with the same layer structure and the same geometry and show an increased magnetoresistive effect (GMR) and

- That in each of the bridge elements (E1 to E4; Ej) a bias layer part (2) and a conductor layer (6, 6i) are provided, this conductor layer (6, 6i) for guiding a setting current (I _e ) predetermined direction and Strength is provided such that an orientation direction of the magnetization (mfj) can be permanently set in the bias layer part (2).

2. Sensor according to claim 1, characterized in that by means of the setting current (I _e ) in the conductor layer (6, 6i) of each bridge element (E1 to E4; Ej) the bias layer part (2) has a magnetic field with a fixed setting of the orientation direction the magnetization (mfj) of the bias layer part enables starch (H _e ) to be exposed.

3. Sensor according to claim 1, characterized in that each bridge element (E1 to E4; E) is exposed to a magnetic support field of such strength (H _z ) that this support field when superimposed with the means of the adjusting current (I _e ) in the conductor layer (6, 6i) to be generated magnetic field (H _e ) the fixed setting of the orientation direction of magnetization (mfj) of the bias layer part (2).

4. Sensor according to claim 3, characterized in that of the bridge elements (El to E4; Ej) located in the supporting field of the predetermined strength (H _z ) in the bias layer parts (2) of two elements (El, E4) on the basis of their predetermined setting currents (I _c ) the predetermined orientation direction of the magnetization (I _e ) at the same time the predetermined orientation direction of the magnetization (mfj) can be set, while in the other elements (E2, E3) on the basis of different setting currents no orientation is possible.

5. Sensor according to one of claims 1 to 4, d a d u r c h g e k e n n z e i c h n e t that means for setting elevated temperature conditions in the orientation of the bias layer parts (2) of the bridge elements (E1 to E4; Ej) are provided.

6. Sensor according to one of claims 1 to 5, so that the conductor layer (6, 6i) consists of an electrically highly conductive material and is applied to a passivation layer (5) covering the layer structure (S, S ').

7. Sensor according to one of claims 1 to 6, characterized in that the layer structure (S, S ') of each bridge element (E1 to E4, Ej) has a magnetic field-sensitive measuring layer (3) and a bias layer part (2) with at least one compared to the Measuring layer (3) has comparatively magnetically harder bias layer (2a).