Sensor device and method for operating a sensor device

Abstract

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

Description

Technical Field

[0001] This invention relates to a sensor device and a method for operating the sensor device. In particular, this invention relates to a sensor device having a magnetoresistive sensor element. Background Technology

[0002] Magnetic field sensors are used to detect magnetic fields. Among these, the so-called magnetoresistive sensor is well-known. This utilizes the fact that the resistance of a particular material changes with a change in an external magnetic field. Furthermore, the resistance also changes due to mechanical forces (tension or pressure) on the sensor element. This effect is known as the magnetoelastic effect.

[0003] For example, publication DE 10236983 A1 describes a magnetic sensor assembly that has a sensor layer sensitive to magnetic fields in an integrated multilayer system, wherein the resistance changes with the external magnetic field. Summary of the Invention

[0004] This invention provides a sensor device having the features of the independent patent claims, as well as a method for operating the sensor device. Other advantageous embodiments are the subject of the dependent patent claims.

[0005] Accordingly, the following settings are configured: A sensor device having a microelectromechanical system (MEMS) and at least one sensor device. The MEMS is designed to apply tensile and compressive forces to the at least one sensor device. Each of the at least one sensor device includes four magnetoresistive sensor elements. In each of the at least one sensor device, the four sensor elements are arranged in the form of a Wheatstone bridge. Accordingly, a first magnetoresistive sensor element is arranged between a positive voltage power supply connection and a first node. A second magnetoresistive sensor element is arranged between the first node and a negative voltage power supply connection. A third magnetoresistive sensor element is arranged between the positive voltage power supply connection and a second node. A fourth magnetoresistive sensor element is arranged between the second node and a negative voltage power supply connection. The reference magnetic field directions of the first, second, third, and fourth sensor elements of the sensor device are all oriented in the same direction. The preferred directions of the first and third sensor elements of the sensor device are oriented opposite to the preferred directions of the second and fourth sensor elements of the corresponding sensor devices. Furthermore, the reference magnetic field directions and preferred directions of all sensor elements of the at least one sensor device are located in a common predetermined plane.

[0006] In addition, the following settings are also provided: A method for operating a sensor device, particularly a sensor device according to the invention. The method includes the step of detecting a first voltage between a first node and a second node of at least one sensor device, wherein pressure is applied to the at least one sensor device via a microelectromechanical system (MEMS). In another step, a second voltage between the first node and the second node of the at least one sensor device is detected while the at least one sensor device is subjected to tension via the MEMS. Furthermore, the method includes the step of determining the magnetic field strength using the detected first and second voltages.

[0007] Advantages of the present invention A magnetoresistive sensor can determine the electric field strength of an applied magnetic field based on the change in resistance as a function of the applied magnetic field. The magnetoresistive sensor can define a plane, which is defined by the orientation of the sensor's preferred direction (easy axis) and the pinning direction of a reference magnetic field. The applied magnetic field may have a component extending parallel to this plane (in-plane component) and a component extending perpendicular to this plane (out-of-plane component).

[0008] Identifying the corresponding portions of the magnetic field vector is challenging. In particular, it is best to obtain all portions of the magnetic field vector simultaneously, if possible. This makes it possible to implement a triaxial sensor as a single integrated structural element.

[0009] Here, the present invention utilizes the fact that, in addition to the change in resistance with the applied magnetic field, the resistance of a magnetoresistive sensor element also changes with the applied tension or pressure. By selectively applying tension and pressure to the sensor element, the sensor signal obtained by the magnetoresistive sensor element can be evaluated according to the concept of the present invention, so as to simultaneously detect external magnetic fields and external forces and determine the magnetic field and force without their interaction. Based on this concept, a sensor device can also be realized to achieve three-dimensional detection of magnetic fields. In particular, the various spatial directions of the magnetic field in three-dimensional space can be determined by a single monolithic sensor.

[0010] To detect the magnetic field, at least one sensor device is configured, in which four magnetoresistive sensor elements are arranged in the form of a Wheatstone bridge. Here, the reference magnetic field direction (fixed direction) and initial preferred direction (easy axis) of all sensor elements lie in a common plane, and the initial preferred directions of all sensor elements are also oriented in the same way. The reference magnetic field directions of diagonally opposite sensor elements are also oriented in the same way, while two sensor elements connected in series have opposite reference magnetic field directions.

[0011] These sensor devices can be deflected perpendicular to the aforementioned common plane via microelectromechanical systems (MEMS). In this way, tension or pressure can be applied to each sensor element.

[0012] By evaluating the voltages at two nodes of each sensor device, combined with the known deflection and the associated force applied to the sensor element, the individual components of the magnetic field in the predetermined plane and perpendicular to the predetermined plane can be separated. In this way, the magnetic field components in each spatial direction can be determined individually.

[0013] According to one embodiment, the sensor device includes a plurality of sensor devices. The plurality of sensor devices can be divided into at least two groups. A first group of sensor devices includes at least one sensor device. Similarly, a second group of sensor devices also includes at least one sensor device. Here, the sensor elements in the two groups of sensor devices are arranged such that the preferred direction of the sensor elements in the first group of sensor devices is perpendicular to the preferred direction of the second group of sensor devices. In this way, mutually orthogonal magnetic field components can be determined in the aforementioned predetermined plane using the two groups of sensor devices.

[0014] According to one embodiment, the first group of sensor devices includes two sensor devices. Similarly, the second group of sensor devices also includes two sensor devices. The four sensor elements can be arranged, for example, at the corners of a virtual rectangle or virtual rhombus, particularly a square. Here, the two sensor elements in one group are arranged diagonally opposite each other. In this way, a particularly advantageous arrangement of the sensor devices can be achieved.

[0015] According to one embodiment, the microelectromechanical system (MEMS) includes a coil. The coil windings can be arranged, for example, in the aforementioned predetermined plane. The coil can be designed to deflect the MEMS and at least one sensor device in a direction perpendicular to the predetermined plane. In this way, easily maneuverable deflection of the sensor device can be achieved to apply tensile or compressive forces.

[0016] According to one embodiment, the coil includes a ferromagnetic element. This ferromagnetic element can improve the design of the current-carrying coil or the force applied thereon.

[0017] According to one embodiment, the sensor device includes a processing device. The processing device may be designed to detect the voltage between a first node and a second node of at least one sensor device, respectively. Furthermore, the processing device can determine the value of the magnetic field strength using one or more detected voltages. Optionally, external forces on the sensor device (particularly sensor elements) can also be determined using voltage, if necessary.

[0018] According to one embodiment, the processing device is designed to determine separate values ​​of the magnetic field strength for mutually orthogonal spatial directions. Specifically, values ​​of the magnetic field strength parallel to and perpendicular to the predetermined plane can be determined separately. When multiple sensor devices are oriented differently, multiple (two) components of the magnetic field strength can also be determined in this plane.

[0019] According to one implementation, the processing device is designed to manipulate microelectromechanical structures (MEMS). This can be achieved, for example, by applying a defined current to coils within the MEMS.

[0020] 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.

[0021] The above-described configurations and extensions—where reasonable—can be combined arbitrarily with each other. Other configurations, extensions, and implementations of the invention include combinations of features of the invention not explicitly mentioned but previously or hereinafter described with reference to embodiments. In particular, those skilled in the art will add individual aspects as improvements or supplements to the corresponding basic forms of the invention. Attached Figure Description

[0022] Other features and advantages of the invention will be described below with reference to the accompanying drawings. As shown herein: Figure 1a , 1b A schematic diagram of the angle and direction generated in the sensor element of a sensor device according to one embodiment; Figure 2 : A schematic diagram of a sensor device according to one embodiment of a sensor apparatus; Figure 3a , 3b 3c: A graph used to illustrate the relationship between voltage and magnetic field or mechanical force at a sensor device; Figure 4 : A schematic cross-sectional view of a sensor device 1 according to one embodiment; Figure 5 : A schematic diagram of a cross-section of a sensor device according to another embodiment; Figure 6 A schematic diagram of a possible arrangement of sensor devices in a sensor apparatus according to one embodiment; and Figure 7 : A flowchart based on a method for operating a sensor device according to another embodiment. Detailed Implementation

[0023] Figure 1aA schematic diagram of a magnetoresistive sensor element 11 according to one embodiment is shown. Here, the magnetization direction (pinning direction) of the reference plane is marked by arrow 21. This direction will be referred to below as the reference magnetic field direction.

[0024] The initial magnetization direction of the free plane, hereinafter referred to as the easy axis, is indicated by arrow 22. When an external magnetic field is applied, magnetization is generated in the free plane, indicated by arrow 23. When a mechanical force is applied, magnetization is generated in the free plane, indicated by arrow 24.

[0025] The resulting resistance R1 can therefore be derived from the following formula: Here, R(θ0) represents the resistance of the sensor element under the influence of an external magnetic field or force. ΔR describes the difference between the maximum and minimum resistance values. Angles θ0, θmag, and θstress are... Figure 1a The angles between the reference magnetic field direction and the preferred direction, the angle between the reference magnetic field direction and the magnetization under the external magnetic field, and the angle between the reference magnetic field direction and the magnetization under the external force are shown and represented.

[0026] Figure 1b A schematic diagram of a magnetoresistive sensor element 12 according to one embodiment is shown. According to... Figure 1b Configuration and basis Figure 1a The difference from the previously described configuration is that the reference magnetic field direction is rotated by 180°, i.e., oriented in the opposite direction. Therefore, for the resistor R2 in this configuration, we get: Figure 2 A schematic diagram of a sensor device 10 having four sensor elements 11 to 14 according to one embodiment is shown. The first sensor element 11 is arranged between the connection terminal of the positive power supply voltage VCC and the first node K1. The second sensor element 12 is arranged between the first node K1 and the connection terminal of the negative power supply voltage or the reference potential GND. Parallel to this, the third sensor element 13 is arranged between the connection terminal of the positive power supply voltage VCC and the second node K2. The fourth sensor element 14 is arranged between the second node K2 and the connection terminal of the negative power supply voltage or the reference potential GND. This circuit configuration is, for example, referred to as a Wheatstone bridge.

[0027] Here, the first sensor element 11 and the fourth sensor element 14 correspond to... Figure 1a The configuration orientation. The second sensor element 12 and the third sensor element 13 correspond to the configuration orientation according to... Figure 1b The configuration is oriented accordingly.

[0028] Therefore, for the first sensor element 11 and the fourth sensor element 14, the resistance is calculated as R1 = R0 - ΔRmag. For the second and third sensor elements 12 and 13, the resistance is calculated as R2 = R0 + ΔRmag. Therefore, in the absence of external mechanical force, a reference voltage V_ref appears between the second node K2 and the first node K1 corresponding to the external magnetic field.

[0029] When an external tensile force is applied to the sensor elements 11 to 14 of the sensor device 10, the resistance R1 of the first and fourth sensor elements 11 and 14 is calculated as R1 = R0 – ΔRmag - ΔRstress. Correspondingly, the resistance R2 of the second and third sensor elements 12 and 13 is calculated as R2 = R0 – ΔRmag + ΔRstress. The voltage between the second node K2 and the first node K1 is referred to as V1 below.

[0030] When an external pressure is applied to the sensor elements 11 to 14 of the sensor device 10, the resistance R1 of the first and fourth sensor elements 11 and 14 is calculated as R1 = R0 – ΔRmag + ΔRstress. Correspondingly, the resistance R2 of the second and third sensor elements 12 and 13 is calculated as R2 = R0 – ΔRmag - ΔRstress. The voltage between the second node K2 and the first node K1 is referred to as V2 below.

[0031] Therefore, when a corresponding force is applied to the sensor device 10, the voltage between the second node K2 and the first node K1 will also change. Since the voltage between the two nodes K2 and K1 changes in the same way but with opposite signs due to tension or pressure, this arrangement allows for the simultaneous determination of external mechanical force and magnetic field.

[0032] Figure 3a A graph is shown to illustrate the relationship between the output voltage V_out measured at nodes K2-K1 and the direction of the resulting angle θmag. The output voltage V_out shown here corresponds to the average of the voltage V1 under applied pressure and the voltage V2 under applied tension: V_out = (V1 + V2) / 2.

[0033] Figure 3b A diagram is shown to illustrate the previous combination. Figure 2 The relationship between the voltage difference V1 – V2 and the direction of the resulting angle θmag is described.

[0034] Figure 3c A diagram is shown to illustrate the previous combination. Figure 2This describes the relationship between the voltage difference V1 – V2 and the direction of the resulting angle θstress. For this purpose, it is assumed that the fixed angle θmag is 70 degrees.

[0035] according to Figure 3a The relationship shown in -c demonstrates a strong linear relationship between the output voltages at the first and second nodes K1 and K2 and the mechanical force. Based on the simulated relationship, it is possible to simultaneously detect external magnetic fields and mechanical forces, and to consider these two effects without them interacting with each other.

[0036] Figure 4 A schematic cross-sectional view of a sensor device 1 according to one embodiment is shown. A MEMS structure 30 may be disposed on a substrate, such as a MEMS substrate 40 having an opening or cavity 41. One or more sensor devices 10 may be disposed at or within this MEMS structure 30. Possible examples of the arrangement of these sensor devices 10 will be described in more detail below.

[0037] Furthermore, the MEMS structure 30 may also include a coil 31. By applying current to the windings of the coil 30, the MEMS structure 30 can be deflected. In this way, tension or pressure can be applied to the sensor device 10. If necessary, a ferromagnetic element 32 may also be additionally provided. The ferromagnetic element 32 may, for example, be arranged inside the coil 31.

[0038] also, Figure 4 The diagram also shows an external magnetic field 4, which has an in-plane component Hx and an out-of-plane component Hz.

[0039] Figure 5 A schematic diagram of a cross-section of a sensor device 1 according to another embodiment is shown. Figure 5 The structure shown in the upper middle region is combined here (in simulated form) with the previous one. Figure 4 The described structure corresponds accordingly. Furthermore, according to... Figure 5 The sensor device 1 also includes a substrate 50, such as a silicon substrate, in the lower region. In this way, for example, the cavity 41 in the MEMS structure 40 can be sealed off, thereby protecting it from external influences.

[0040] Furthermore, an integrated circuit, such as an application-specific integrated circuit (ASIC), can be disposed in the substrate 50. This circuit can, for example, provide the required voltage VCC to the sensor device 10. Additionally, this circuit can detect and process the voltage between nodes K1 and K2. If necessary, the coil 31 can also be manipulated via this circuit. Therefore, the deflection of the MEMS structure 30 for applying the desired force to the sensor device 10 and the evaluation of the signals generated thereat at nodes K1 and K2 of the sensor device 10 can be easily synchronized.

[0041] For external contact, a suitable contact element 51 can be provided on the substrate 50.

[0042] Figure 6 A schematic top view of a MEMS substrate 30 for a sensor device 1 according to one embodiment is shown. Figure 6 As can be seen, for example, four sensor devices 10-i can be arranged equidistantly, for example, at the corners of a virtual square. Here, for example, sensor devices 10-i that are diagonally opposite each other can be oriented in the same way, while sensor devices 10-i that are adjacent to each other through the edge of the virtual square are arranged by rotating 90 degrees.

[0043] In particular, the reference magnetic field direction and the preferred orientation of all sensor elements 11-14 can lie in a common plane.

[0044] With this arrangement, the orientation of the magnetic field in all three spatial directions, x, y, and z, can be determined. For example, sensor devices 10-1 and 10-4 can detect the magnetic field components in the y and z directions, while two other sensor devices 10-2 and 10-3 can detect the magnetic field components in the x and z directions.

[0045] Figure 7 A flowchart illustrating a method for operating a sensor device according to one embodiment is shown. This method can be implemented particularly when using one of the sensor devices 1 described above. Therefore, the description previously given in conjunction with Figures 1 to 6 applies to the method described below. Similarly, the sensor device 1 described above may also include any components necessary for implementing the method described below.

[0046] K1K2 In step S1, when pressure is applied through the microelectromechanical structure 30, a first voltage V1 between the first node K and the second node K2 of at least one sensor device 10 is detected.

[0047] In step S2, when a tensile force is applied through the microelectromechanical structure 30, the voltage between the first node K1 and the second node K2 of at least one sensor device 10 is detected.

[0048] After the voltage is detected, the value of the external magnetic field strength can be obtained in step S3. The value of the magnetic field strength can be obtained specifically when using the detected voltage. Here, individual values ​​can be obtained for each spatial direction in three-dimensional space.

[0049] The component of the external magnetic field extending parallel to the plane defined by the preferred direction and the reference magnetic field direction (the component in the plane) is obtained here from the average of the first voltage V1 and the second voltage V2: (V1+V2) / 2. The component of the external magnetic field perpendicular to the plane is obtained from the difference between the first voltage V1 and the second voltage V2: V1-V2.

[0050] In summary, the present invention relates to a sensor element for three-dimensional detection of a magnetic field using magnetoresistive sensor elements. To this end, a sensor device is proposed in which at least one assembly having four magnetoresistive sensor elements in the form of a Wheatstone bridge can be deflected by a microelectromechanical structure to apply mechanical force to the sensor elements.

Claims

1. A sensor device (1), comprising: At least one sensor device (10), each of which has four magnetoresistive sensor elements (11-14). as well as Microelectromechanical structure (30), said microelectromechanical structure being designed to apply tensile or compressive forces to sensor elements (11-14) of said at least one sensor device (10), In each sensor device (10), a first magnetoresistive sensor element (11) is arranged between the positive voltage power supply connection terminal (VCC) and the first node (K1), a second magnetoresistive sensor element (12) is arranged between the first node (K1) and the negative voltage power supply connection terminal (GND), a third magnetoresistive sensor element (13) is arranged between the positive voltage power supply connection terminal (VCC) and the second node (K2), and a fourth magnetoresistive sensor element (14) is arranged between the second node (K2) and the negative voltage power supply connection terminal (GND). Among them, the reference magnetic field directions of the first, second, third, and fourth sensor elements (11-14) are all oriented in the same direction. The preferred orientations of the first and fourth sensor elements (11, 14) are opposite to the preferred orientations of the second and fourth sensor elements (12, 13). The reference magnetic field direction and preferred direction of all sensor elements (11-14) are in a common predetermined plane.

2. The sensor device (1) according to claim 1, wherein, The sensor device (1) includes multiple sensor devices (10). The first group of sensor devices includes at least one sensor device (10). The second group of sensor devices includes at least one sensor device (10). The preferred orientation of the sensor elements (11-14) of the first group of sensor devices is perpendicular to the preferred orientation of the second group of sensor devices.

3. The sensor device (1) according to claim 2, wherein, The first group of sensor devices includes two sensor devices (10). The second group of sensor devices includes two sensor devices (10).

4. The sensor device (1) according to any one of claims 1 to 3, wherein, The microelectromechanical structure (30) includes a coil (31) designed to deflect the microelectromechanical structure (30) and the at least one sensor device (10) in a direction perpendicular to the predetermined plane.

5. The sensor device (1) according to claim 4, wherein, The coil (31) includes a ferromagnetic element (32).

6. A sensor device (1) having a processing device, the processing device being designed to detect the voltage between a first node (K1) and a second node (K2) of the at least one sensor device (10), and to determine the value of the magnetic field strength using one or more detected voltages.

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

8. The sensor device (1) according to claim 6 or 7, wherein, The processing device is also designed to manipulate the microelectromechanical structure (30).

9. The sensor device (1) according to any one of claims 1 to 8, wherein, The processing device is implemented as a dedicated integrated circuit in the sensor device (1).

10. A method for operating a sensor device (1), wherein, The sensor device (1) comprises the sensor device (1) according to any one of claims 1 to 9, and the method comprises the following steps: When pressure is applied through the microelectromechanical structure (30), the voltage between the first node (K1) and the second node (K2) of at least one sensor device (10) is detected (S1); When a tensile force is applied through the microelectromechanical structure (30), the voltage between the first node (K1) and the second node (K2) of at least one sensor device (10) is detected (S2); and The value of the magnetic field strength (S3) is obtained using the detected voltage.

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