Sensor for the detection of the direction of a magnetic field

(54) Title: SENSOR FOR THE DETECTION OF THE MEANING OF A MAGNETIC FIELD AND ANGULAR SENSOR (51) Int.CI .: G01B7 / 30; H02K29 / 08; H01L43 / 06 (30) Unionist Priority: 8/21/2000 CH 2000 1645/00 (73) Holder (s): Melexis Technologies SA, Melexis Tessenderlo NV, Sentron AG.

(72) Inventor (s): Christian Schott, Radivoje Popovic, Robert Racz

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SENSOR FOR THE DETECTION OF THE MEANING OF A MAGNETIC FIELD AND ANGULAR SENSOR

The invention relates to a sensor for detecting the direction of a magnetic field of the type mentioned in the generic concept of claim 1.

Such a sensor is suitable, for example, for application as an angular sensor in the control of brushless electric motors that have a stator with several coils. The rotor of the electric motor has a permanent magnet that interacts with the sensor to generate a signal to control the coils according to the phases and that depends on the rotation angle. This type of provision is known in the European patent application EP 954 085. As a sensor, a vertical Hall element with several arms is used, with each arm generating a Hall voltage depending on the position of the permanent magnet. Hall voltages are used to control the motor coils

<td>electric. 0</td><td>Hall element</td><td>vertical</td><td>and</td><td>sensitive to</td>

<td>components</td><td colspan="2">of the magnetic field created by the</td><td>magnet</td><td>permanent and</td>

<td colspan="2">that are parallel to the surface</td><td>the chip.</td><td>He</td><td>presents the</td>

<td>disadvantage</td><td>of not being able to be</td><td>accomplished</td><td>at the</td><td>same chip,</td>

together with the electronic processing circuit, since it is based on a special semiconductor technology.

It is also known to use horizontal Hall elements, sensitive to the components of the magnetic field created by the permanent magnet, which manifest themselves vertically on the surface of the chip. These Hall elements can be integrated on the same chip as the electronic processing circuit. However, this is a solution that has the disadvantage that Hall elements have to be

2/15 arranged in the marginal area of ​​the permanent magnet, where the vertical components of the magnetic field have greater intensity. In the area of ​​the rotary axis, the vertical components are therefore of low intensity. The placement of Hall elements depends on the dimensions of the permanent magnet. In the case of larger permanent magnets, it is not profitable to integrate Hall elements on a single chip.

An angular sensor with a magnetic field sensor element based on the effect of magnetoresistance is known in European patent application EP 893 66 8. There is also a horizontal Hall element, which allows the measurable angular range to be raised to more than 180 °. 0 Hall element, however, has to be positioned in a different place from the magnetic field sensor element, because, while the magnetic field sensor element has to measure the horizontal components of the magnetic field of the rotating permanent magnet, the Hall element has to measure its vertical elements. Sensors based on the effect of magnetoresistance also have hysteresis effects, which, in turn, limit the dispersion capacity.

From the European patent application EP 772 046, a magnetic field sensor that is sensitive to magnetic fields arranged parallel to the chip surface and realizable on a semiconductor chip, together with the electronic circuit, is known. With this type of magnetic field sensor, it is possible to measure only a single component of the magnetic field.

The invention aims to suggest a sensor that does not have the above mentioned disadvantages.

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The invention has the characteristics cited in claim 1. An advantageous design is the result of the subordinate claims.

According to the first aspect of the invention, the sensor comprises, for detecting the direction of a magnetic field, only a single flat-field concentrator and at least one first and second Hall element or at least one first and second group of elements Hall, and the Hall elements are arranged in the marginal area of ​​the magnetic field concentrator.

The flat magnetic field concentrator has the task of influencing an external magnetic field in such a way that it passes through the Hall elements in an ideal way.

Hall elements can be horizontal or vertical. Horizontal Hall elements are sensitive to the components of the magnetic field that appear vertically on its surface, while vertical Hall elements react to a component of the magnetic field parallel to its surface. For this reason, the horizontal Hall elements should be arranged below the magnetic field concentrator and vertical Hall elements in the area near the edge, outside the magnetic field concentrator.

According to another aspect of the invention, the sensor for detecting the direction of a magnetic field comprises at least three magnetic field concentrators symmetrically arranged in a plane with respect to a point of symmetry, which has in the area of ​​the point of symmetry ends facing one for the others, in parallel, in addition to a Hall element or a group of Hall elements per magnetic field concentrator, the elements of

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Hall are arranged in the area of ​​the parallel ends of the respective magnetic field concentrator.

In the following, the invention will be explained in more detail, with the aid of drawings.

The following is shown:

Fig. 1 - a first example of a sensor with horizontal Hall elements consistent with the invention.

Fig. 2 - sensor with a cut along line II in Fig. 1.

Fig. 3 - a second example of a sensor consistent with the invention.

Fig. 4 - Details of the sensor.

Fig. 5, 6 - an example of a sensor with elements of

Vertical halls consistent with the invention.

Fig. 7a, b - sensors consistent with the invention, through which the direction of the external magnetic field can be determined in three dimensions, and

Fig. 8-11 - other sensors consistent with the invention.

Fig. 1 shows a top view of a sensor consistent with the invention, suitable, for example, as an angular sensor for controlling a brushless electric motor with three coils. The sensor comprises a semiconductor chip (1) with six horizontal Hall elements (2.1 to 2.6) and a single magnetic field concentrator (3). In this first example, the magnetic field concentrator (3) is disk-shaped and the six elements of Hall 2 are spread out at uniform distances along the edge (4) of the magnetic field concentrator (3).

Hall elements (2.1 to 2.6) are made with

5/15 technology generally known, preferably with CMOS technology as doped well n (6) (Fig. 2) on a substrate p doped (Fig. 2). The horizontal Hall elements are sensitive to the magnetic field components that appear vertically on the surface (8) of the semiconductor chip (1). In the example, the Hall elements (2.1 to 2.6) have a cross-shaped structure, the alignment of which is preferably parallel to the crystal axis, so that the influence of variable mechanical stresses on the Hall signal is kept as low as possible. possible.

magnetic field concentrator (3) is composed of ferromagnetic material, preferably Permalloy or Mumetall or a metallic glass, which, for example, can be purchased in the thickness of about 15 μιπ to 30μπι. Preferably, a metallic glass with a relatively low coercive field is employed, so that hysteresis effects do not arise. In addition, its magnetization is completely isotropic.

magnetic field concentrator (3) extends in a plane (9) and has a flat shape, that is, its thickness is considerably less than its extension in the plane. The magnetic field concentrator (3) preferably has a uniform thickness. However, it can be thicker in the center than at the edge. The magnetic field concentrator (3) therefore acts as a concentrator for the magnetic field components that are in the plane (9). 0 operation of the magnetic field concentrator (3) is explained in more detail through fig. 2. In this example, the magnetic field concentrator

6/15 of symmetry (5) which (3) has a rotationally symmetric center.

Fig. 2 shows the sensor in a section along line II of fig. 1, in addition to a permanent magnet (10) which is mounted on the axis (11) of a brushless electric motor (12) with three coils and which generates a magnetic field. The magnetic field concentrator (3) alters the course of the lines of the field (13) of the magnetic field, making, in particular, the lines of the field, which in the absence of a magnetic field concentrator (3) would run in parallel to the surface (8) of the semiconductor chip (1), pass through the Hall element (2.1) almost vertically to the surface (8). The relative permeability of the magnetic field concentrator material (3) is greater than 1000, while the air and semiconductor permeability (7) is approximately 1.

Field lines are almost always vertical to the surface of the magnetic field concentrator (3). The Hall elements (2.1 to 2.6) are arranged in the area of ​​the lateral edge (4) of the magnetic field concentrator (3), since in this position the vertical component of the magnetic field has the largest dimension.

The Hall elements positioned opposite to each other, diametrically in relation to the center of symmetry (5) (fig. 1) form pairs for the generation of the output signal, with the Hall voltage of one of the elements of Hall is subtracted from the Hall voltage of the other element. Because the field lines penetrate both Hall elements of a pair in the opposite vertical direction, the stresses arising through the deviation of the magnetic field are from the substrate

Therefore,

7/15 added together, while Hall tensions, arising, for example, due to an external parasitic field that penetrates Hall elements, cancel each other out. In addition, offset stresses conditioned by technology are at least partially offset. The Hall elements (2.1) and (2.4) therefore generate the output signal Si together, the Hall elements (2.2) and (2.5) generate the output signal S₂ and the Hall elements (2.3) and (2.6) generate the output signal S₃. The intensity of the output signals Si, S₂ and S₃depends on the direction of the magnetic field in the plane (9).

If the permanent magnet (10) rotates around the axis (11), the magnetic field rotates together, generating, for example, the sinusoidal output signals S₂, S₂ and S₃, which have a 120 ° lag. The output signal Si assumes the maximum value whenever the direction of the magnetic field of the permanent magnet (10) is parallel to the axis that joins the Hall elements (2.1) and (2.4), the output signal S₂ assumes the maximum value whenever the direction of the magnetic field of the permanent magnet (10) is parallel to the axis that joins the elements (2.3) and (2.5), etc. The output signals Si, S₂ and S₃, as described in the European patent application EP 954085, can be used to control the three coils of the electric motor (12).

However, the output signals Si, S₂ and S₃ they can also be used to determine the rotation angle &lt;p of the shaft (11), if the electric motor (12) is stopped. At this point, it is important that, as far as possible, no signal is superimposed on the output signals Si, S₂ and S₃which do not come from the magnetic field of the permanent magnet (10). The suggested example with the elements of

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Hall combined in pairs is especially suitable for this case, as interference from external fields is completely eliminated and offset stresses conditioned by technology are fully compensated. Offset stresses conditioned by technology can be further reduced when, instead of the isolated Hall elements (2.1 to 2.6), groups of two or more Hall elements are used, the current direction being different in the various elements of a group.

An example of this type is illustrated by fig. 3, in which there are four groups (14 to 17), each with two Hall elements (2.1 to 2.8). The groups of Hall elements, positioned opposite each other, diametrically, are combined in pairs, so that the sensor provides two output signals Si and S₂. This means, therefore, that the Hall voltages of the Hall elements (2.1), (2.2), (2.5) and (2.6) form the output signal Si and the Hall voltages of the elements (2.3), (2.4). , (2.7) and (2.8) the output signal S₂. In fig. 3, the Hall elements are shaped like a cross and each Hall element has been assigned an arrow that indicates the direction of flow within the element. In this example, the magnetic field concentrator (3) also has a cross-shaped structure, which makes the concentration of the magnetic field at the location of the Hall elements greater than in the previous example with the circular structure. This sensor is suitable, for example, for operating an electric motor (12) with two coils. If necessary, it is possible to memorize the value of the output signals Si and S₂ depending on the rotation angle φ. Because the output signals S_x and S₂ out of phase, the angle of

9/15 rotation φ can be easily and uniquely determined using the output signals Si and S₂.

Fig. 4 illustrates schematically and not faithful to the scale, referring to the sensor of the first example, the semiconductor chip (1) with both Hall elements (2.1) and (2.4) integrated, which are positioned diametrically opposite one of the another, in a plane in relation to the axis (11) (see also fig. 1), in addition to the circular magnetic field concentrator (3). The vertical arrows indicate the intensity and direction of the field created by the permanent magnet (10) (fig. 2) in the area of ​​the two Hall elements (2.1) and (2.4). A displacement of the magnetic field concentrator (3) from the ideal position in the positive x direction causes a reduction in the Hall voltage in the element (2.1) and an increase in the Hall voltage in the element (2.4). An advantage is that the diameter of the magnetic field concentrator (3) has been adapted to the two Hall elements (2.1) and (2.4) in such a way that both elements (2.1) and (2.4), with the magnetic field concentrator ( 3) in the ideal position in reference to the two Hall elements (2.1) and (2.4), they are not in the zone, in which the intensity of the magnetic field reaches its maximum value: The Hall elements (2.1) and (2.4) are positioned close to the center, as shown in fig. 4, or away from the center. The influence of variations in the positioning of the magnetic field concentrator (3) in relation to the two Hall elements (2.1) and (2.4) is thus minimized.

If the sensor is used only to control an electric motor, the rotation angle at the motor stop is not important, it is sufficient that it is available

10/15 only one of the Hall elements joined as a pair. In the first realization example, these Hall elements are (2.1), (2.2) and (2.3).

Instead of a circular magnetic field concentrator, a concentrator with another shape, such as polygonal, can also be used. Especially for photoiitographic reasons, it may be convenient to approach the circular shape using a polygon. Likewise, the number of Hall elements can be increased.

Fig. 5 shows an example of an embodiment with vertical Hall elements (2). Vertical Hall elements are sensitive to the magnetic field components that penetrate the Hall element parallel to the surface (8) of the semiconductor chip (1). An example of a Hall element that can be integrated into the electronic circuit is described in US patent 5,572,058. The vertical Hall elements (2) are aligned tangentially to the edge (4) of the magnetic field concentrator (3). They are located in the area of ​​the edge (4) of the magnetic field concentrator (3), but not below the magnetic field concentrator (3), where the field lines (13) of the magnetic field (fig. 2) parallel to the surface (8) of the semiconductor chip (1) are larger.

Fig. 6 indicates by means of arrows the intensity of the horizontal lines (13) (fig. 2) of the magnetic field in the area of ​​the vertical Hall elements (2), the length of the arrow being proportional to the intensity of the magnetic field.

The advantages of these solutions over solutions known in the current technical standard are as follows:

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a) The position of the Hall elements in relation to the permanent magnet is not critical, as the hall elements do not have to be positioned on the edge of the permanent magnet, where the vertical component of the magnetic field is greater, but in the area of ​​the rotating axis , where the horizontal components are larger, so that the positioning of the semiconductor chip, in which the Hall elements are integrated, can occur regardless of the position of the permanent magnet's edge.

b) The magnetic field concentrator additionally reinforces the magnetic field in the area of ​​the Hall elements.

c) Hall elements and the electronic processing circuit can be integrated on the same semiconductor chip.

d) Deviation from the actual position of the magnetic field concentrator in relation to its theoretical position, within the common manufacturing tolerances, has no influence on the generated signals.

The sensors described are also suitable as an angular sensor for the applications described in the European patent application EP 893 668 mentioned above.

Fig. 7a shows a third example of a sensor corresponding to the invention, in which the magnetic field concentrator (3) has the shape of a ring. This allows the disposition of another horizontal Hall element (2 '), for example, in the center of the ring, through which it is possible to measure the components of the magnetic field that run parallel to the Hall element (2'). This type of sensor is suitable, for example, for application on a joystick, as this way the direction of the field

12/15 external magnetic can be determined in a three-dimensional way.

Because the magnetic field concentrator (3) is very thin, it practically does not influence the magnetic field component that falls vertically on the Hall element (2 '). Also with the sensor shown in fig. 7b it is possible to determine the direction of the external magnetic field in three dimensions. However, there is a danger here that horizontal components will overlap the vertical component, since, firstly, the magnetic field concentrator (3) reinforces the horizontal components and, secondly, in case of changes in the theoretical position of the magnetic field concentrator, horizontal components of the magnetic field can penetrate the Hall element (2 ') in the vertical direction.

It should be noted that in the example illustrated by fig. 7a, the magnetic field concentrator (3) can also act as a concentrator for the vertical component of the magnetic field, just then when the width of the ferromagnetic ring is comparable to its thickness. From the sum of the signals from the two Hall elements (2.1) and (2.3) or from the sum of the signals from the two Hall elements (2.2) and (2.4), one can obtain a signal that is proportional to the vertical component of the field magnetic, while the difference, as shown above, allows the determination of horizontal components. The Hall element (2 ') can even be suppressed.

A single Hall element requires a relatively small area of ​​a few tens of micrometers. The diameter of the magnetic field concentrator so

Circular 13/15 is approximately 0.2 to 0.5 mm. In the ideal case, the diameter of the magnetic field concentrator is smaller than the diameter of the permanent magnet, which is normally 1.3 mm or larger.

Usually, an external field above 20 mT causes a saturation effect in the magnetic field concentrator. If the theoretical distance between the permanent magnet and the sensor is selected in such a way that the magnetic field concentrator is at least partially saturated, it has the advantage that the output signals Si and S₂, etc. they do not depend or little depend on distance variations of the permanent magnet of the sensor.

It is also possible to apply the Hall elements as pulse emitters, in which case the rotating permanent magnet generates as many impulses as the number of existing Hall elements.

Fig. 8 shows an angle sensor with three magnetic field concentrators (18.1), (18.2) and (18.3), which, like the sensor in the first example, together with a permanent magnet with an angle emitter effect, is suitable as an angle sensor for the command of an electric motor of. three coils. The magnetic field concentrators (18.1), (18.2) and (18.3) are arranged symmetrically in relation to a point of symmetry (19), more precisely with a rotation symmetry of 120 °. In the edge area (4) of each magnetic field concentrator facing the point of symmetry (19) there is a horizontal Hall element (2.1), (2.2) or (2.3). The edge (4) of the magnetic field concentrators is subdivided and, two areas, more precisely an internal area, in which edges

14/15 (20) of the concentrators (18.1), (18.2) and (18.3) arranged opposite each other assume a parallel position, in order that the density of the lines of the magnetic field is as homogeneous as possible in the gap between both edges (20 ) and a saturation of the tips is avoided, and an external area, in which the distance between neighboring magnetic field concentrators is too large, in order to prevent the magnetic field from being short-circuited here. The outer edge (21) of the magnetic field concentrators (18.1), (18.2) and (18.3) disperses as wide an area as possible, in order to concentrate the outer magnetic field as efficiently as possible in the area of ​​the elements of Hall (2.1), (2.2) or (2.3) and avoid saturation peaks, which could influence the angular dependence of the signals. In this example, each element of Hall (2.1), (2.2) or (2.3) emits a signal Si, S₂ or S₃.

Instead of isolated Hall elements (2.1), (2.2) or (2.3), groups of Hall elements that have already had an offset correction between them can be predicted.

Figs. 9 and 10 show two other sensors with four magnetic field concentrators (18.1) to (18.4), with which the direction of a magnetic field can be determined in two spatial dimensions. Here, two Hall elements positioned opposite and diametrically, in relation to the point of symmetry (19) are joined as a pair: the Hall elements (2.1) and (2.3) together generate the output signal Si; elements (2.2) and (2.4) together generate the output signal S₂. Through the output signals Si and S₂ it is possible to determine the direction of the magnetic field in the plane (9) of the sensor.

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In the sensors shown in fig. 8 to 10, magnetic field concentrators do not have to be flat. They can have a greater thickness at the edge or be coupled to additional external magnetic field concentrators, in order to concentrate the field

<td>magnetic in the area of</td><td>elements</td><td>from Hall</td><td colspan="2">the way</td><td>more</td>

<td>efficient as possible.</td><td></td><td></td><td></td><td></td><td></td>

<td>Fig. 11 shows</td><td>An example</td><td colspan="2">of achievement</td><td>with</td><td>three</td>

<td>field concentrators</td><td>magnetic</td><td> (18.1),</td><td> (18.2) ,</td><td> (18 .</td><td>.3) and</td>

<td>10 three elements of Hall</td><td>vertical</td><td> (2.1),</td><td> (2.2),</td><td> (2.3)</td><td>what</td>

are respectively arranged in the center, between the parallel edges (20) of the concentrators (18.1), (18.2), (18.3).

While the examples of realization and applications of this invention have been shown and described, it is clear to experts that these models bring with them other possibilities for modification, more than it was possible to explain above, without abandoning the design of the invention. Therefore, the invention should not be restricted, except with respect to the claims.

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