Sensor device and method for operating a sensor device

Abstract

The invention relates to a sensor element for the three-dimensional detection of a magnetic field by means of magnetoresistive sensor elements. To this end, a sensor device is proposed in which at least one assembly with four magnetoresistive sensor elements in the form of a Wheatstone bridge can be deflected by means of a microelectromechanical structure in order to exert a mechanical force on the sensor elements.

Description

[0001] Description

[0002] title

[0003] Technical area

[0004] The present invention relates to a sensor device and a method for operating a sensor device. In particular, the present invention relates to a sensor device with magnetoresistive sensor elements.

[0005] background

[0006] Magnetic field sensors are used to detect magnetic fields. Among these sensors are so-called magnetoresistive sensors. These sensors take advantage of the fact that the electrical resistance in a certain material can change depending on an external magnetic field. Furthermore, the resistance can also change due to a mechanical force (tensile or compressive force) acting on the sensor element. This effect is known as the magnetoelastic effect.

[0007] The document DE 102 36 983 A1, for example, describes a magnetic sensor arrangement with a magnetic field-sensitive sensor layer in an integrated multi-layer system, wherein the electrical resistance changes depending on an external magnetic field.

[0008] Disclosure of the invention

[0009] The present invention provides a sensor device and a method for operating a sensor device having the features of the independent patent claims. Further advantageous embodiments are the subject of the dependent patent claims.

[0010] Accordingly, it is provided:

[0011] A sensor device with a microelectromechanical structure (MEMS) and at least one sensor device. The MEMS is designed to exert a tensile force and a compressive force on the at least one sensor device. Each of the at least one sensor device comprises four magnetoresistive sensor elements. In each of the at least one sensor device, the four sensor elements are each arranged in the form of a Wheatstone bridge. Accordingly, a first magnetoresistive sensor element is arranged between a positive voltage supply terminal and a first node. A second magnetoresistive sensor element is arranged between the first node and a negative voltage supply terminal. A third magnetoresistive sensor element is arranged between a positive voltage supply terminal and a second node.A fourth magnetoresistive sensor element is arranged between the second node and the negative voltage supply terminal. The reference magnetic field directions of the first, second, third, and fourth sensor elements of a sensor device are each aligned identically. The preferred directions of the first and third sensor elements of a sensor device are aligned opposite to the preferred directions of the second and fourth sensor elements of the respective sensor device. Furthermore, the reference magnetic field directions and the preferred directions of all sensor elements of the at least one sensor device lie in a common predetermined plane.

[0012] Furthermore, it is planned:

[0013] A method for operating a sensor device, in particular a sensor device according to the invention. The method comprises a step of detecting a first electrical voltage between the first node and the second node of the at least one sensor device, wherein a compressive force is applied to the at least one sensor device by the microelectromechanical structure. In a further step, a second electrical voltage is detected between the first node and the second node of the at least one sensor device, while the at least one sensor device is subjected to a tensile force by the microelectromechanical structure. Furthermore, the method comprises a step of determining a value for a magnetic field strength using the detected first and second voltages.

[0014] Advantages of the invention

[0015] Magnetoresistive sensors are capable of determining a value for the electric field strength of the applied magnetic field based on a change in electrical resistance as a function of an applied magnetic field. The magnetoresistive sensors can define a plane spanned by the orientation of the preferred direction (easy axis) and the reference magnetic field direction (pinning direction) of the respective sensors. The applied magnetic field can have magnetic field components that run parallel to this plane (in-plane components) and magnetic field components that run perpendicular to this plane (out-plane components).

[0016] Identifying the individual components of a magnetic field vector presents a challenge. In particular, it is desirable to determine the individual components of a magnetic field vector as simultaneously as possible. This enables the implementation of a 3-axis sensor as a single integrated component.

[0017] The present invention takes advantage of the fact that magnetoresistive sensor elements, in addition to a variation in electrical resistance depending on an applied magnetic field, also vary in electrical resistance depending on an applied tensile or compressive force. By deliberately applying tensile and compressive forces to the sensor elements, the inventive concept makes it possible to evaluate the sensor signals determined by the magnetoresistive sensor elements in order to simultaneously detect an external magnetic field and an external force, while determining the magnetic field and force in a decoupled manner. Based on such a concept, it is also possible to create a sensor device for implementing three-dimensional detection of a magnetic field. In particular, the individual spatial directions of a magnetic field in three-dimensional space can be determined using a single monolithic sensor.

[0018] To detect the magnetic field, at least one sensor device is provided, in which four magnetoresistive sensor elements are arranged in the form of a Wheatstone bridge. The reference magnetic field directions (pinning direction) and the initial preferred directions (easy axis) of all sensor elements lie in a common plane, with the initial preferred directions of all sensor elements also being aligned identically. The reference magnetic field directions of diagonally opposite sensor elements are also aligned identically, while any two sensor elements connected in series have opposite reference magnetic field directions.

[0019] These sensor devices can be deflected perpendicular to the common plane described above using a microelectromechanical system (MEMS). In this way, a tensile or compressive force can be exerted on the individual sensor elements.

[0020] By evaluating the electrical voltages at the two nodes of the individual sensor devices in combination with the known deflection and the associated force exerted on the sensor elements, it is then possible to separate the individual components of the magnetic field in the predetermined plane as well as perpendicular to the predetermined plane.

[0021] In this way, the magnetic field components for each spatial direction can be determined individually.

[0022] According to one embodiment, the sensor device comprises a plurality of sensor devices. The plurality of sensor devices can be divided into at least two groups. A first group of sensor devices comprises at least one sensor device. Likewise, a second group of sensor devices comprises at least one sensor device. The sensor elements in the two groups of sensor devices are arranged such that the preferred directions of the sensor elements of the first group of sensor devices are aligned perpendicular to the preferred directions of the second group of sensor devices. In this way, mutually orthogonal components of the magnetic field can be determined by the two groups of sensor devices in the predetermined plane described above.

[0023] According to one embodiment, the first group of sensor devices comprises two sensor devices. The second group of sensor devices also comprises two sensor devices. The four sensor elements can be arranged, for example, at the corners of a virtual rectangle or a virtual rhombus, in particular a square. The two sensor elements of a group are each arranged diagonally opposite one another. In this way, a particularly advantageous arrangement of the sensor devices can be achieved.

[0024] According to one embodiment, the microelectromechanical structure comprises a coil. The windings of the coil can, for example, be arranged in the predetermined plane described above. The coil can be designed to deflect the microelectromechanical structure with the at least one sensor device in a direction perpendicular to the predetermined plane. In this way, an easily controlled deflection of the sensor devices for applying a tensile or compressive force can be achieved.

[0025] According to one embodiment, the coil comprises a ferromagnetic element. Such a ferromagnetic element can increase the design and the force exerted by the current-carrying coil.

[0026] According to one embodiment, the sensor device comprises a processing device. The processing device can be configured to detect an electrical voltage between the first node and the second node of the at least one sensor device. Furthermore, the processing device can determine a value for a magnetic field strength using the detected voltage(s). Optionally, an external force acting on the sensor device, in particular the sensor elements, can also be determined using the electrical voltages.

[0027] According to one embodiment, the processing device is designed to determine individual values ​​of the magnetic field strength for mutually orthogonal spatial directions. In particular, values ​​for the magnetic field strength parallel to the predetermined plane described above and perpendicular to this predetermined plane can be determined. If several sensor devices are oriented differently, several (two) components of the magnetic field strength can also be determined in this plane.

[0028] According to one embodiment, the processing device is designed to control the microelectromechanical structure. This can be done, for example, by applying a defined current to a coil in the MEMS.

[0029] According to one embodiment, the processing device is implemented as an application-specific integrated circuit (ASIC) in the sensor device. For example, such an integrated circuit can be implemented directly in a substrate coupled to the MEMS.

[0030] The above embodiments and further developments can be combined with one another as desired, where appropriate. Further embodiments, further developments, and implementations of the invention also include combinations of features of the invention not explicitly mentioned above or described below with respect to the exemplary embodiments. In particular, those skilled in the art will also add individual aspects as improvements or additions to the respective basic forms of the invention.

[0031] Short description of the drawings

[0032] Further features and advantages of the invention are explained below with reference to the figures, in which: Fig. 1 a, 1 b: schematic representations of the resulting angles and

[0033] Directions in sensor elements for a sensor device according to an embodiment;

[0034] Fig. 2: a schematic representation of a sensor device for a

[0035] Sensor device according to an embodiment;

[0036] Fig.3a, 3b, 3c: Diagrams illustrating the relationships between electrical voltage at the sensor devices and the magnetic fields or mechanical forces;

[0037] Fig. 4: a schematic representation of a cross section through a

[0038] Sensor device 1 according to an embodiment;

[0039] Fig. 5: a schematic representation of a cross section through a

[0040] Sensor device according to another embodiment;

[0041] Fig. 6: a schematic representation of a possible arrangement of

[0042] Sensor devices in a sensor device according to an embodiment; and

[0043] Fig. 7: a flowchart underlying a method for operating a sensor device according to a further embodiment.

[0044] Description of embodiments

[0045] Figure 1a shows a schematic representation of a magnetoresistive sensor element 11 according to one embodiment. The magnetization direction of the reference plane (pinning direction) is indicated by arrow 21. This direction is referred to below as the reference magnetic field direction.

[0046] The initial magnetization direction of the free plane is referred to as the preferred direction (“easy axis”) and is shown by the arrow 22. When subjected to an external magnetic field, this results in a magnetization in the free plane, which is shown by the arrow

[0047] 23 is shown. When a mechanical force is applied, a magnetization results in the free plane, which is shown by the arrow 24.

[0048] The resulting electrical resistance R1 is therefore given by the following formula:

[0049] AR

[0050] RI = R(0O) - —cos(ßmag — Ostress)

[0051] Here, R(0O) denotes the resistance of the sensor element under the influence of an external magnetic field or an external force. ΔR describes the difference between the maximum and minimum values ​​of the electrical resistance. The angles ΔO, Δmag, and Δstress are shown in Figure 1a and denote the angle between the reference magnetic field direction and the preferred direction, the angle between the reference magnetic field direction and the magnetization in the presence of an external magnetic field, and the angle between the reference magnetic field direction and the magnetization in the presence of an external force.

[0052] Figure 1b shows a schematic representation of a magnetoresistive sensor element 12 according to one embodiment. The configuration according to Figure 1b differs from the previously described configuration according to Figure 1a in that the reference magnetic field direction is rotated by 180°, i.e., oriented in the opposite direction. Thus, the resulting electrical resistance R2 in this configuration is:

[0053] AR

[0054] R2 = R(0O) - — cos((180° — 0mag) + Ostress

[0055] Figure 2 shows a schematic representation of a sensor device 10 with four sensor elements 11 to 14 according to one embodiment. A first sensor element 11 is arranged between a terminal for a positive supply voltage VCC and a first node K1. A second sensor element 12 is arranged between the first node K1 and a terminal for a negative supply voltage or a reference potential GND. In parallel, a third sensor element 13 is arranged between the terminal for the positive supply voltage VCC and a second node K2. A fourth sensor element 14 is arranged between the second node K2 and the terminal for the negative supply voltage or the reference potential GND. Such a circuit configuration is known, for example, under the name Wheatstone bridge.

[0056] The first sensor element 11 and the fourth sensor element 14 are aligned according to the configuration shown in Figure 1a. The second sensor element 12 and the third sensor element 13 are aligned according to the configuration shown in Figure 1b.

[0057] For the first sensor element 11 and the fourth sensor element 14, this results in an electrical resistance of R1 = RO - ARmag. For the second and third sensor elements 12, 13, this results in an electrical resistance of R2 = RO + ARmag. Thus, without any external mechanical force, a reference voltage V_ref corresponding to the external magnetic field is established between the second node K2 and the first node K1.

[0058] When an external tensile force is applied to the sensor elements 11 to 14 of the sensor device 10, the electrical resistance R1 of the first and fourth sensor elements 11, 14 results in a value of R1 = RO - ARmag - ARstress. Accordingly, the electrical resistance R2 of the second and third sensor elements 12, 13 results in a value of R2 = RO - ARmag + ARstress. The electrical voltage between the second node K2 and the first node K1 is referred to below as V1.

[0059] When an external compressive force is applied to the sensor elements 11 to 14 of the sensor device 10, the electrical resistance R1 of the first and fourth sensor elements 11, 14 results in a value of R1 = RO - ARmag + ARstress. Correspondingly, the electrical resistance R2 of the second and third sensor elements 12, 13 results in a value of R2 = RO - ARmag - ARstress. The electrical voltage between the second node K2 and the first node K1 is referred to below as V2. Thus, when the sensor device 10 is subjected to a corresponding force, the electrical voltage between the second node K2 and the first node K1 also changes. Since the electrical voltage between the two nodes K2 and K1 changes in the same way due to tensile or compressive force, an external mechanical force and a magnetic field can be determined simultaneously using such an arrangement.

[0060] Figure 3a shows a diagram illustrating the relationship between the measured output voltage V_out at the node K2-K1 and the direction of the resulting angle 0mag. The output voltage V_out shown corresponds to the average value of the electrical voltage V1 when subjected to a compressive force and the electrical voltage V2 when subjected to a tensile force: V_out = (V1 + V2) / 2.

[0061] Figure 3b shows a diagram illustrating the relationship between a difference between the voltages V1 - V2 previously described in connection with Figure 2 and the direction of the resulting angle 0mag.

[0062] Figure 3c shows a diagram illustrating the relationship between a difference between the voltages V1 - V2 described previously in connection with Figure 2 and the direction of the resulting angle Ostress. A fixed angle 0mag of 70 degrees was assumed for this purpose.

[0063] According to the relationships shown in Figures 3a-c, a good linear relationship can be seen between the output voltage at the first and second nodes K1, K2 as a function of the mechanical force. Based on the simulated relationships shown, it is thus possible to simultaneously detect an external magnetic field and a mechanical force and to observe the two effects in isolation from each other.

[0064] Figure 4 shows a schematic representation of a cross-section through a sensor device 1 according to one embodiment. A MEMS structure 30 can be provided on a substrate, for example, a MEMS substrate 40 with an opening or cavity 41. One or more sensor devices 10 can be provided on or in this MEMS structure 30. A possible example of an arrangement of these sensor devices 10 is described in more detail below.

[0065] Furthermore, the MEMS structure 30 can comprise a coil 31. By applying an electric current to the windings of this coil 30, the MEMS structure 30 can be deflected. In this way, tensile or compressive forces can be exerted on the sensor devices 10. If necessary, a ferromagnetic element 32 can also be provided. This ferromagnetic element 32 can, for example, be arranged inside the coil 31.

[0066] Furthermore, Fig. 4 shows the external magnetic field 4 with the in-plane components Hx and the out-plane component Hz.

[0067] Figure 5 shows a schematic representation of a cross-section through a sensor device 1 according to another embodiment. The structure shown in the upper area of ​​Figure 5 corresponds (in a simulated form) to the structure previously described in connection with Figure 4. Furthermore, the sensor device 1 according to Figure 5 comprises a substrate 50, for example, a silicon substrate, in the lower area. In this way, for example, the cavity 41 in the MEMS structure 40 can be sealed and thus protected from external influences.

[0068] Furthermore, it is also possible to provide an integrated circuit, for example, an application-specific integrated circuit (ASIC), in the substrate 50. This circuit can, for example, supply the sensor devices 10 with the required voltage VCC. Furthermore, the circuit can detect and process the electrical voltages between the nodes K1 and K2. If necessary, the coil 31 can also be controlled using this circuit. Thus, the deflection of the MEMS structure 30 for applying a desired force to the sensor devices 10 and the evaluation of the resulting signals at the nodes K1 and K2 of the sensor devices 10 can be easily synchronized.

[0069] For external contacting, suitable contact elements 51 can be provided on the substrate 50.

[0070] Figure 6 shows a schematic top view of an ME MS substrate 30 for a sensor device 1 according to one embodiment. As can be seen in Figure 6, for example, four sensor devices 10-i can be arranged equidistantly, for example, at the corners of a virtual square. In this case, diagonally opposite sensor devices 10-i can, for example, be aligned identically, while the sensor devices 10-i of adjacent sensor devices across the edges of the virtual square are each arranged rotated by 90 degrees.

[0071] In particular, the reference magnetic field directions and the preferred directions of all sensor elements 11 - 14 can lie in a common plane.

[0072] With such an arrangement, it is possible to determine the orientation of a magnetic field in all three spatial directions: x, y, and z. For example, sensor devices 10-1 and 10-4 can detect magnetic field components in the y and z directions, while the other two sensor devices 10-2 and 10-3 can detect magnetic field components in the x and z directions.

[0073] Figure 7 shows a flowchart underlying a method for operating a sensor device according to one embodiment. The method can be carried out, in particular, using one of the previously described sensor devices 1. Thus, the statements already made in connection with Figures 1 to 6 apply to the method described below. Similarly, the previously described sensor devices 1 can also include any components that may be required to implement the method described below.

[0074] K1 K2

[0075] In a step S1, a first electrical voltage V1 is detected between the first node K and the second node K2 of the at least one sensor device 10 when a compressive force is applied by the microelectromechanical structure 30.

[0076] In step S2, an electrical voltage is detected between the first node K1 and the second node K2 of the at least one sensor device 10 when a tensile force is applied by the microelectromechanical structure 30.

[0077] After detecting the electrical voltages, a value for an external magnetic field strength can be determined in step S3. The value of the magnetic field strength can be determined, in particular, using the detected voltages. Individual values ​​can be determined for each spatial direction of a three-dimensional space.

[0078] The external magnetic field component for the plane parallel to the plane spanned by the preferred direction and the reference magnetic field direction (in-plane component) results from the mean value of the first voltage V1 and the second voltage V2: (V1 + V2) / 2. The external magnetic field component perpendicular to this plane results from the difference between the first voltage V1 and the second voltage V2: V1 - V2.

[0079] In summary, the present invention relates to a sensor element for three-dimensional detection of a magnetic field using magnetoresistive sensor elements. For this purpose, a sensor device is proposed in which at least one arrangement with four magnetoresistive sensor elements in the form of a Wheatstone bridge can be deflected by means of a microelectromechanical structure in order to exert a mechanical force on the sensor elements.

Claims

Claims 1. A sensor device (1), comprising: at least one sensor device (10), each having four magnetoresistive sensor elements (11-14); and a microelectromechanical structure (30) designed to exert a tensile force or compressive force on the sensor elements (11-14) of the at least one sensor device (10), wherein in each sensor device (10), a first magnetoresistive sensor element (11) is arranged between a positive voltage supply terminal (VCC) and a first node (K1), a second magnetoresistive sensor element (12) is arranged between the first node (K1) and a negative voltage supply terminal (GND), a third magnetoresistive sensor element (13) is arranged between a positive voltage supply terminal (VCC) and a second node (K2),and a fourth magnetoresistive sensor element (14) is arranged between the second node (K2) and the negative voltage supply terminal (GND), wherein reference magnetic field directions of the first, second, third and fourth sensor elements (11-14) are each aligned the same, wherein preferred directions of the first and fourth sensor elements (11, 14) are aligned opposite to the preferred directions of the second and fourth sensor elements (12, 13), and, wherein the reference magnetic field directions and the preferred directions of all sensor elements (11-14) lie in a common predetermined plane.

2. Sensor device (1) according to claim 1, wherein the sensor device (1) comprises a plurality of sensor devices (10), wherein a first group of sensor devices comprises at least one sensor device (10), and a second group of sensor devices comprises at least one sensor device (10), and wherein the preferred directions of the sensor elements (11-14) of the first group of sensor devices are aligned perpendicular to the preferred directions of the second group of sensor devices.

3. Sensor device (1) according to claim 2, wherein the first group of sensor devices comprises two sensor devices (10), and the second group of sensor devices comprises two sensor devices (10).

4. Sensor device (1) according to one of claims 1 to 3, wherein the microelectromechanical structure (30) comprises a coil (31) which is designed to deflect the microelectromechanical structure (30) with the at least one sensor device (10) in a direction perpendicular to the predetermined plane.

5. Sensor device (1) according to claim 4, wherein the coil (31) comprises a ferromagnetic element (32).

6. Sensor device (1) with a processing device which is designed to generate an electrical voltage between the first node (K1) and the second node (K2) of the at least one Sensor device (10) and to determine a value for a magnetic field strength using the detected voltage or voltages.

7. Sensor device (1) according to claim 6, wherein the processing device is designed to determine individual values ​​of the magnetic field strength for mutually orthogonal spatial directions.

8. Sensor device (1) according to claim 6 or 7, wherein the processing device is further configured to control the microelectromechanical structure (30).

9. Sensor device (1) according to one of claims 1 to 8, wherein the processing device is implemented as an application-specific integrated circuit in the sensor device (1).

10. A method for operating a sensor device (1), wherein the sensor device (1) comprises a sensor device (1) according to one of claims 1 to 9, comprising the steps: Detecting (S1) an electrical voltage between the first node (K1) and the second node (K2) of the at least one sensor device (10) when a compressive force is applied by the microelectromechanical structure (30); Detecting (S2) an electrical voltage between the first node (K1) and the second node (K2) of the at least one sensor device (10) when a tensile force is applied by the microelectromechanical structure (30); and Determining (S3) a value for a magnetic field strength using the detected voltages.

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