AT407803B - Magnetic field sensor - Google Patents

Abstract

The invention relates to a magnetic field sensor having a large number of magnetoresistive resistors 10 which are arranged on a mount or on a substrate 30 in order to form a sensor array, and which are possibly each equipped with barb pole structures 11, a remagnetisation line 12 and/or a compensation line 13. The invention provides for the overall outline 21 of the sensor array 40 or of the magnetically active area of the sensor 40 which is occupied by the resistors 10, in a plane parallel to the mount or to the substrate 30, to have the outline or the circumferential shape 41 of an ellipse, or to approximate to the outline or to the circumferential shape of an ellipse. <IMAGE>

Description

AT 407 803 B

The invention relates to a magnetic field sensor according to the preamble of claim 1.

Magnetoresistive sensors of this type, e.g. are known from US 5,485,334 A or JP-8-203032 A, are used for measuring weak to medium magnetic fields. Depending on the direction of magnetization with respect to the direction of current flow in a thin film, its ohmic resistance is influenced by an external magnetic field, which is used to determine this external field.

A large number of disturbances can be eliminated by suitable switching of the resistors formed from thin magnetic films. This is done, for example, by means of a Wheatstone bridge circuit of four resistance groups, with the spontaneous magnetization of the films being periodically reversed (flipped) (this causes a current-carrying conductor loop, which is formed from a thin flip conductor), and the change in resistance caused by the magnetic field to be measured is considered as Alternating signal tapped at the bridge output.

Furthermore, it is known to compensate for the magnetic field to be measured at the location of the sensor by means of compensation conductors, as a result of which the sensor works as a zero indicator and the result is independent of the sensor characteristic in a first approximation. Flip and compensation conductors can be integrated on a sensor chip and due to the proximity of the current-carrying conductor layers to the resistance films, even weak currents are sufficient for these auxiliary fields.

A decisive disadvantage of these structures is the fact that the field acting inside the magnetoresistive film is generally less than the external magnetic field to be measured. This should be clarified in the following. The spatial position of the spontaneous magnetization essentially depends on the geometric shape of the layer. Free magnetic poles can occur at the geometric boundary of the film, causing a stray field with non-negligible energy. Stray fields could be completely avoided by closed flux rings. However, these flux rings lead, for example in the case of alloy compositions which are not magnetostriction-free, to considerable magnetostrictive stressing of the crystal, so that in general complete freedom from stray fields is not optimal in terms of energy. In addition, a domain structure in magnetoresistive layers is anyway undesirable because of the poorly reproducible magnetization process.

The effective field Hi in the layer results in the external field Ha with the demagnetizing field He due to the demagnetization tensor Ne and the magnetization

Mzu H, = Ha + He = Ha -Ne-M.

MdV

Ne can be represented as the sum of the geometric demagnetization tensor NeG and a tensor Ne, which results from inhomogeneities in the layer and is called the internal demagnetization tensor. Ne, can only be considered statistically. For the energy in the stray field:

Strictly speaking, these equations only apply on the condition that a homogeneous external field results in a homogeneous magnetization in the layer, and this magnetization in turn results in a homogeneous demagnetizing field. Exactly, this only applies to homogeneous, ellipsoidal samples. For a general ellipsoid with the main axes A, B and C in the main position, the demagnetization tensor becomes a diagonal matrix with the elements Na, Nb and N0. These geometric demagnetization factors can be calculated for the three axis directions using elliptical integrals. It applies

Na + Nb + Nc = 1. The energy EF in the stray field then depends on the direction cosine axyz of the magnetization with respect to the ellipsoid axes:

2

AT 407 803 B

In order to overcome this so-called shape anisotropy energy EF, work has to be done from the external field, which ultimately turns the magnetization in the direction of the field. In addition, the inner field will not be homogeneous in the edge regions of, for example, a rectangular layer, and the coherent rotation of the magnetization will be disturbed.

This problem is solved according to the invention in a magnetic field sensor of the type mentioned at the outset by the features stated in the characterizing part of patent claim 1. There are improvements in sensitivity and the signal-to-noise ratio, the demagnetizing field is minimized and the homogeneous field conditions mean that the spontaneous magnetization is coherent up to the edge areas. These improvements are supported when proceeding according to the features of claim 2. The effect of the overall arrangement of the resistors is increased with the features of claim 5.

The layers or films forming the resistors can be applied in several steps in order to approximately achieve the spatial shape of an ellipsoid or semi-ellipsoid for the sensor field, as a result of which the field conditions are homogeneous on the inside and the magnetization rotation is also coherent in the edge regions. For example, an approximately ellipsoidal or semi-ellipsoidal structure of the sensor field can be produced in a simple manner by means of vapor deposition technology and various elliptical masks.

Sensor noise can occur in particular in the case of high-resolution measurement of very weak fields, and the invention therefore proposes to proceed in accordance with the features of patent claims 3 and 4. The use of the features according to claim 6 is advantageous for improving the resolution and sensitivity.

It is not only particularly advantageous to make the sensor field approximately elliptical or an ellipse in at least one plane parallel to the base or to the support and, if necessary, to design the overall spatial shape of the sensor field in the form of an ellipsoid or a semi-ellipsoid, but it can also According to the invention, the individual resistors forming the sensor field, which are spaced apart on the base, are formed approximately in at least one plane parallel to the base or an ellipse. It is advantageous to proceed according to one of claims 7 to 11.

It is particularly easy to build up the ellipsoidal or semi-ellipsoidal structure of a sensor field if the individual resistors forming the sensor field are built up from layers, the resistances lying outside in the sensor field being made up of fewer layers or being made up of thinner layers than the layers closer to the center of the sensor field. The layer thickness or the number of layers from which a resistor is built up can be varied as desired by means of appropriate vapor deposition techniques.

Further advantageous embodiments of the invention can be found in the following description, the drawings and the patent claims.

The invention is explained in more detail below, for example, with reference to the drawings.

1 and 1a schematically show a magnetic field sensor according to the invention in plan view and in longitudinal section. Fig. 2 shows the interaction of individual magnetic quantities in a magnetized ellipsoid. Fig. 3 shows the amount of the demagnetizing magnetic field. 4 schematically shows the structure of an ellipsoidal sensor field. 5 schematically shows the layer structure of a magnetic field sensor according to the invention. Fig. 6 shows schematically the structure of a single, ellipsoidal resistor. 7a and 7b schematically show a longitudinal and a cross section through a semi-ellipsoidal resistor. 8 shows a schematic section through an embodiment of a magnetoresistive resistor. Fig. 9 shows a section through a series of resistors.

1 shows a schematic plan view of a magnetic field sensor with a structure which is known in principle. The series-connected magnetic resistance films or resistors 10 are provided with well-conductive barber pole structures 11 with strips 11a in order to achieve a current flow of approximately 45 ° for spontaneous magnetization in order to optimize the operating point. The barber pole structures 11 can be applied on the bottom and / or on the top of the resistors 10; at least the application of a barber pole structure on the side of the resistor 10 facing away from the carrier or the base 30 is sufficient.

A short current pulse in the flip conductor or in the magnetic reversal line 12 defines the third

AT 407 803 B

Direction of the magnetization M in the resistors 10. The field of the compensation line 13, which can be seen from the section according to FIG. 1 a, is used to compensate the field Ha to be measured at the location of the resistors 10. According to the schematic section in FIG. 1 a, at least one shielding layer 15 or 18 is provided or formed between the magnetic reversal line 12 and the compensation line 13 and / or between the compensation line 13 and the resistor 10. This shielding layer 15 or 18 can be formed by one or more electrically conductive, optionally insulated film layers. The shielding layers 15 and 18 are advantageously grounded in alternating current. An insulation layer J is expediently formed on at least one side of the shielding layer 15 or 18, so that the compensation line 13 and the magnetic reversal line 12 are separated by the shielding layers 15 or 18 and the insulation layers J or are electrically shielded from the resistors or resistance layers 10. If necessary, only one of the two shielding layers 15 or 18 can be provided, in particular if the mutual influence of the magnetic reversal line 12 and the compensation line 13 is irrelevant for the measurement result.

The resistors 10 provided can be connected in series or as a potentiometer or as a bridge; the circuit depends on the respective application of the magnetic field sensor.

It is noted that the representations are not to scale.

The procedure according to the invention can advantageously also be used for simple magnetic field sensors which consist only of a magnetically active layer or a magnetoresistive resistor (for example cores of flux gates, simple magnetoresistive resistors, flux guiding layers for Hall probes ...).

Fig. 2 shows the interaction of the fields Ha, Hh He and M in a magnetized ellipsoid. In the long main axis, the demagnetizing field is minimal and thus the sensitivity of the sensor is increased.

3 shows the magnitude of the demagnetizing field He of a rod-shaped (long ellipsoid) and a disk-shaped sample (flat ellipsoid).

Ha becomes minimal both along the rod axis and in the disc plane.

4 schematically shows the structure of an ellipsoidal sensor field 40. The sensor field 40 has an elliptical contour 41 in a plane parallel to the carrier 30. This ellipse has a large axis A and a small axis B. Within this ellipse-shaped outline 41, a large number of resistors 10 are arranged and overall approximately fill the area of an ellipse. The elliptical resistors 10 lie with their longer axis A perpendicular to the long axis A of the ellipse 41 or the long axis A of the spaced-apart resistors 10 runs parallel to the short axis B of the sensor field 40. As shown schematically, the sensor field 40 has one Section parallel to the axis A and parallel to the axis B advantageously also an elliptical cross-sectional shape or a cross-sectional shape that approximates an ellipse as possible. In this connection it is noted that the sensor field 40 can also have the shape of a semi-ellipsoid or that in this case the cutting planes along the axes A and B have the outline shape of a semi-ellipse or are as close as possible to this outline shape.

The desired cross-sectional shape of the sensor field 40 in planes parallel to the axes A and B is achieved by correspondingly varying the thicknesses or heights h of the individual resistors 10 on the carrier 30 or by building up ellipsoids in a carrier layer.

In the production of such a sensor field 40, a number of preferably elliptical or approximately elliptical circumferential magnetoresistive resistors 10 are applied to a base 30 in such a way that these resistors in the directions of the axes A and B of the sensor field 40 are parallel or mutually perpendicular are aligned.

As shown in FIG. 9, the bottom layer 21 of a resistor 10 is first applied to a carrier 30, further layers 23, 25 etc. being applied to this layer 21 in each case. These further layers 23, 25, 27 have smaller dimensions in particular with respect to the semiaxes. The thickness and the length of the semiaxes of the layers 21, 23, 25, 27 are coordinated with one another in such a way that elliptical cross-sectional shapes result for the resistors 10 in the respective side or sectional views, as is particularly the case in FIG. 4

AT 407 803 B the FIGS. 7a and 7b is shown in more detail. It is advantageous if not only the sensor field 40 has an elliptical or semi-ellipsoidal shape, but also the individual resistors 10 forming the sensor field have an ellipsoidal or semi-ellipsoidal shape. FIG. 9 shows a section along the axis B of a sensor field 40 according to FIG. 4, the external resistors 10 being constructed from two layers 21, 23; the inner row of resistors consists of three layers 21, 23 and 25; the inner layer consists of four layers 21, 23, 25 and 27; from this middle layer the number of layers of the individual resistors 10 decreases again towards the outside. A similar structure of the resistors can also be carried out along the individual rows of resistors parallel to the axis A. Since the thickness of the individual layers can also be varied, with the large number of resistors 10 present along axis A, the layers of the resistors located in the outer regions of sensor field 40 can be thinner or have a lower height h, or the thickness can increase in the direction axis B be different than in the direction of axis A. Ultimately, however, the resistances located on the outer circumference of the elliptical sensor field should have approximately the same height from one another or the resistances 10 located in the central region of the ellipse should have a substantially comparable height from one another.

The approximation to the shape of a semi-ellipsoid is easier to implement for the sensor field, because in the production of the lower half of an ellipsoid supporting layers adjacent to the magnetoresistive layer are necessary in order to be able to planarly apply elliptical layers with increasing semi-axes. In any case, it is essential that the resistors 10 in the middle of the sensor field are thicker than those in the edge zones, which ensures the almost ellipsoidal structure of the sensor field and at the same time achieves an approximately homogeneous field distribution within the sensor.

The number of layers forming the resistors 10 depends on the required accuracy and on the manufacturing effort. The axis ratio or the axes A, B and C of the sensor field 40 are not shown to scale in FIG. 4, but exaggerated. In order to achieve a low demagnetization factor in the plane of the sensor field 40, the ellipsoid is advantageously designed to be very flat. For this reason, in many cases three layers for the resistors 10 will suffice.

Fig. 5 shows schematically a section through a magnetic field sensor according to the invention similar to Fig. 1a, in which between the thin layers 10, 18, 13, 15 and 12 each passivation layers P and / or adhesive layers H and / or insulation layers J, the latter, in particular for insulation the shielding layers 15, 18 are arranged. Depending on the desired shielding effect, one or two shielding layers 15 or 18 are provided. Depending on the materials used and the type of production, these layers are bonded to one another by means of appropriate adhesion promoter layers H and / or passivation layers P in order to achieve a compact structure which is electrically insulated from one another in each case.

6 schematically shows the structure of an ellipsoidal resistor 10. A lowermost magnetoresistive layer 21, preferably with an elliptical outline, is applied to the base 30 or the support provided, with a non-magnetic layer 22 of the same thickness around this layer 21 by means of appropriate masking and coating is arranged around. In the next coating step, a further layer 23, preferably an elliptical layer with larger semiaxes, is applied to these applied layers 21, 22 directly above the first layer 21, the edge of which is followed by a further, non-magnetic layer 24, etc. It is possible in this way to produce an at least perpendicular and transverse to the base 30 ellipsoidal resistor 10. The thickness of the individual layers and the length of the semiaxes of the layers 21, 23, ..., which are preferably also elliptical parallel to the base 30, are advantageously coordinated with one another in such a way that all

Side views result in an approximately elliptical cross section and thus the spatial shape of an ellipsoid is approximated as closely as possible.

A semi-ellipsoid is constructed in the same way, except that the layer with the largest elliptical outline is started as the base layer and smaller layers are applied to each of the semi-axes a and b.

The number of layers is determined by the required accuracy and the manufacturing effort. The axial ratio of the ellipses is exaggerated in Fig. 2 and 4a and 4b. 5

AT 407 803 B

In order to achieve a low demagnetization factor in the film plane, the ellipsoid is advantageously designed to be very flat. In most cases, sufficiently homogeneous fields in the resistance layer 10 will be achieved with only three layers.

The sensor field 40 is constructed in such a way that a plurality of resistors 10 are simultaneously formed on a carrier in a correspondingly ellipsoidal or semi-ellipsoidal manner.

7a and 7b show a longitudinal section and a cross section through a resistor 10, which is made up of three layers and approximates a semi-isoid. It can be seen that a flat semi-ellipsoid can be produced or approximated well with just three layers, which can also be varied or graduated with regard to their height or thickness h.

FIG. 8 schematically shows a side view of the structure of a resistance layer or a resistance 10, which is built on a base 30. Current leads 31, 32 are connected to the bottom layer 21 of the resistor 10 in both end regions, which lead over the resistance layer 21 in the end region below and above. Intermediate layers such as Passivation and / or adhesion promoter layers have not been shown to increase clarity. The layer thicknesses are also not drawn to scale. The lower power supply lines 31 can be applied to the electrically insulating substrate or the base 30, for example by means of sputtering, the lower barber structures being dispensed with in the present case. On the upper surface of the magnetoresistive film of the lowermost layer 21, the barber pole strips 11a and in the end regions the upper power supply 32 are applied.

In the depression 35 formed in the lowermost layer 21 by the elevation or step 34 for the connection of the current feeds or discharges 31, 32, the next following magnetoresistive layer 23 can be partially introduced to homogenize the inner field, whereby the desired shape of the Ellipsoids or Halbeliipsoids is approximated. Since this layer 23 reproduces the structure of the strips 11a on its outside, the approximation to an elliptical contour is improved. The gradation in the layer 21 by the lower power supply 31 also contributes to this. These two layers 21, 23 already result in a relatively good structure, approximating an ellipsoid, over which the insulation layer J is applied, to which insulation layer J the further layers follow, as already shown in connection with FIGS. 1 and 5.

If the layer 23 is omitted or no further layers are applied, then the magnetic field compensating power supply 31, 32 also yields advantages for non-ellipsoidal resistors 10.

In Fig. 1, the resistors 10 are shown rectangular in the longitudinal direction; this is done for graphic reasons. The resistors 10 advantageously have an elliptical cross section in a plane parallel to the base 30. It can be seen that the current leads 31, 32 are laterally offset by the individual resistors 10 with respect to the longitudinal axis LA. This laterally offset arrangement takes place with mutually opposite end regions of the resistors 10 on the same side of these resistors 10 or on the same side of the longitudinal axis LA. The power supply lines 31 and 32 are thus approximated to the central region of the first barber pole strip 11a. The current through the or each resistor 10 should, if possible, enclose an angle of 40-50 °, in particular 45 °, with the magnetization (which is parallel to the longitudinal axis). This is achieved by the connection geometry of the current supply lines 31 shown in FIG. 1.

These inventive measures make it possible to optimally compensate for the magnetic fields created by the current flow, and overall improvements in the interference signal distance from magnetoresistive magnetic field sensors are achieved. The ohmic and capacitive effects of the compensation line 13 and the magnetic reversal line 12 on one another and on the resistance films 10 are avoided by the shielding layers 15, 18 which are arranged between these levels. The sensor noise is reduced in particular by the ellipsoidal or semi-ellipsoidal shape of the resistors 10, since in this case the spontaneous magnetization rotates coherently into the edge regions. The disturbing magnetic fields generated by the current leads 31 and 32 and the barber pole structures 11 in the region of the resistors 10 are connected to the barber pole 6 by the double-sided connection and

Claims (16)

AT 407 803 B structures 11 parallel coupling of the current flow avoided. It is noted that the ellipsoidal or semi-ellipsoidal design of the resistors supports the effect or effect which is achieved by the arrangement of the individual resistors in the form of an ellipsoidal or semi-ellipsoidal sensor field 40 er-5. About 100 to 1000 resistors 10 are arranged in a sensor field 40 designed according to the invention. The resistors 10 are arranged at the same or regular, mutual intervals, in particular in the form of a regular network in the sensor field 40. 10 PATENT CLAIMS: 15 20 25 30 35 40 45 50 1. Magnetic field sensor with a large number of magnetoresistive resistors (10) arranged on a carrier or a base (30) to form a sensor field, which are connected to a magnetic reversal line (12) and / or a compensation line ( 13) and optionally with barber pole structures (11) with mutually parallel strips (11a) on the side (30) facing and the opposite side of the respective resistor (10), preferably between the compensation line (13) and the respective one Resistors (10) and / or between the magnetic reversal line (12) and the respective resistors (10) there is at least one electrically conductive shielding layer (15) which is arranged in an electrically isolated manner from the other layers, in particular AC-grounded, characterized in that the overall outline ( 21) of a variety of magne the resistive resistors (10) formed sensor field (40) or the magnetically active area of the sensor (40) occupied by the plurality of resistors (10) in a plane parallel to the carrier or to the base (30) the outline or the peripheral shape (41 ) has an ellipse or approximates the outline or the circumferential shape of an ellipse. 2. Magnetic field sensor according to claim 1, characterized in that the direction of the spontaneous magnetization (M) or the major axis (a) of the individual resistors (10) perpendicular to the longitudinal direction of the sensor field (40) or perpendicular to the major axis (A) of the elliptical outline (41) of the sensor field (40). 3. Magnetic field sensor according to claim 1 or 2, characterized in that the outline or the thickness of the spaced apart resistors (10) formed sensor field (40), at least in a plane perpendicular to the carrier (30) has an elliptical or semi-elliptical shape or approximates the shape of an ellipse or semi-ellipse. 4. Magnetic field sensor according to one of claims 1 to 3, characterized in that the outline or the thickness of the spaced apart resistors (10) formed sensor field (40) in two mutually orthogonal, each perpendicular to the carrier (30) planes, namely in a plane perpendicular to the support (30) and perpendicular to the magnetization (M) and / or in a plane perpendicular to the support (30) and parallel to the magnetization (M) has an elliptical or semi-elliptical shape or approximates the shape of an ellipse or semi-ellipse is. 5. Magnetic field sensor according to one of claims 1 to 4, characterized in that the resistors (10) forming the sensor field (40) in their entirety form at least approximately an ellipsoid or semi-ellipsoid. 6. Magnetic field sensor according to one of claims 1 to 5, characterized in that the ratio of the axes (A, B) of the ellipse is in a range from A: B = 1.5: 1 to A: B = 10: 1 and that the ratio of the two axes (A, B) lying in a plane parallel to the base (30) to the third axis (C) perpendicular to the plane of the carrier (30) in the range from A: C or B: C = 500: 1 up to 5000: 1. 7. Magnetic field sensor according to one of claims 1 to 6, characterized in that the individual, magnetoresistive resistors (10) in planes parallel to the base rectangular) or elliptical (n) or approximately elliptical (n) outline or circumferential shape. 7 55 AT 407 803 B 8. Magnetic field sensor according to one of claims 1 to 7, characterized in that the magnetoresistive resistors (10) consist of several, in particular at least two or three, magnetoresistive layers (21, 12, 25) applied to one another. 9. Magnetic field sensor according to claim 8, characterized in that the resistor (10) forming, successively applied thin layers (23, 25) with respect to the length of their semiaxes (a, b) and / or in terms of their thickness (h) compared to each layer (21, 23) applied immediately below or underneath are reduced. 10. Magnetic field sensor according to claim 8 or 9, characterized in that the superimposed layers (21, 23, .....) of the resistors (10) in a perpendicular to the base and in the longitudinal direction of the layers (21,23 .. ....) extending plane and / or in a plane perpendicular to the base (30) and transverse to the longitudinal direction of the layers (21, 23 ......) the cross-sectional shape (35) of an ellipse or a semi-ellipse or a an approximate cross-sectional shape of an ellipse or semi-ellipse. 11. Magnetic field sensor according to one of claims 7 to 10, characterized in that the formed by the respective resistor (10) or approximated ellipsoid or semi-ellipsoid with semiaxes (a, b) in a plane parallel to the base (30) and a third A semiaxis (c) perpendicular to the base (30) has an axis ratio a: c of greater than 200: 1, preferably greater than 1000: 1, in particular approximately 2000: 1, and an axis ratio b: c of greater than 100: 1 , preferably of greater than 500: 1, in particular of about 1000: 1. 12. Magnetic field sensor according to one of claims 1 to 11, characterized in that connected to the two end regions of the respective resistors (10) current leads (31, 32) comprise the resistor (10) in the respective end region from above and below the top and bottom of the respective end area are connected. 13. Magnetic field sensor according to one of claims 1 to 12, characterized in that at the two end regions of the respective resistors (10) connected current leads (21, 32) with respect to the longitudinal axis (LA) of the resistor (10) on different sides of the longitudinal axis (LA ) are connected offset. 14. Magnetic field sensor according to claim 12 or 13, characterized in that the connection ends of the current leads (31, 32) connected to the two end regions of the respective resistor (10) are each formed parallel to the strips (11a) of the barber pole structure (11). 15. Magnetic field sensor according to one of claims 1 to 14, characterized in that the individual resistors (10) in the sensor field (40) are arranged in the longitudinal and / or in the transverse direction in parallel rows. 16. Magnetic field sensor according to one of claims 1 to 15, characterized in that the resistors (10) located in the outer region of the sensor field (40) are constructed with a smaller number of layers (21, 23 ......) than that central resistors (10). THEREFORE 9 SHEET OF DRAWINGS 8