Sensor circuit and method for compensating for mechanical stress of a magnetoresistive sensor

Abstract

A sensor circuit (300) is provided, comprising a first bridge circuit (310) that includes a plurality of first magnetoresistives (312) with a first reference magnetization along a first directional axis and an output (314) for a first output signal in response to an external magnetic field. The sensor circuit (300) also includes a second bridge circuit (320) that includes a plurality of second magnetoresistives (322) with a second reference magnetization along a second directional axis and an output (324) for a second output signal in response to the external magnetic field. The sensor circuit (300) also includes a sensor (330) configured to measure a physical quantity indicating a reference magnetization rotation of the first and second magnetoresistives (312; 322).The sensor circuit (300) also includes a processing circuit arrangement (340) configured to determine a compensated output signal based on the first output signal, the second output signal and the physical quantity indicating the reference magnetization rotation.

Description

Area

[0001] The present disclosure relates generally to magnetoresistive sensor circuits and in particular to a concept for eliminating or reducing one or more voltage effects in magnetoresistive sensor circuits. background

[0002] The voltage dependence of xMR sensors can manifest as changes in sensitivity and the rotation of the reference system. The "x" in xMR stands for the specific type of magnetoresistance effect used. Common types of xMR sensors include AMR (anisotropic magnetoresistance), GMR (giant magnetoresistance), TMR (tunnel magnetoresistance), and CMR (colossal magnetoresistance) sensors.

[0003] AMR sensors utilize the anisotropic magnetoresistance effect, where electrical resistance changes based on the angle between the direction of current flow and the magnetization within the material. GMR sensors are based on the giant magnetoresistance effect, where electrical resistance changes significantly due to the orientation of magnetization in alternating ferromagnetic and non-magnetic layers. TMR sensors utilize the tunnel magnetoresistance effect, where resistance changes due to the tunneling of electrons between ferromagnetic layers separated by an insulating barrier. The tunneling probability depends on the relative orientation of the magnetizations in the ferromagnetic layers.CMR sensors are based on the colossal magnetoresistance effect observed in some manganese oxide compounds, in which the resistance changes drastically in response to an applied magnetic field.

[0004] In the context of xMR sensors, sensitivity refers to the sensor's ability to detect changes in the magnetic field. It is a measure of how much the sensor's output changes in response to a given change in the magnetic field. Mechanical stress can alter the material properties and magnetic characteristics of the layers within the xMR sensor. This can cause the sensitivity to vary, meaning the sensor responds more or less strongly to changes in the magnetic field. For example, a voltage can lead to changes in the sensor's resistance, which in turn affects the output signal for a given magnetic input.

[0005] In xMR sensors, the reference system typically refers to a fixed magnetic layer that provides a stable reference direction for measuring the relative angle of the free magnetic layer, which is free to rotate in response to external magnetic fields. Mechanical stress can physically deform the sensor, leading to misalignment of the magnetic layers. This deformation can cause the magnetic reference layer to rotate or deviate from its intended orientation. Such rotation affects the accuracy of the sensor's measurements because the reference direction is no longer stable and reliable. This can introduce errors into the measurement of the direction and strength of the external magnetic field.

[0006] This voltage dependence can lead to problems with stray field suppression in speed and current sensors and to orthogonality errors in angle sensors. This refers to the sensor's ability to ignore or filter unwanted magnetic fields (stray fields) that do not originate from a target signal source. Effective stray field suppression is required for accurate measurements in magnetic sensing applications. For example, despite a differential stray field suppression concept, in the worst case, 25% of the stray field can enter the signal path in the orthogonal direction. In the sensitive direction, sensitivity variation of up to 10–15% at different positions on a die can also lead to poor stray field suppression and the inability of speed sensors to operate with wheels where the signal pitch is much larger than the sensor pitch.

[0007] Therefore, there may be a need to eliminate or reduce one or more xMR voltage effects. Summary

[0008] This need is addressed by devices and methods according to the attached claims.

[0009] According to a first aspect, the present disclosure provides a sensor circuit. The sensor circuit comprises a first bridge circuit. The first bridge circuit (half-bridge or full-bridge) comprises a plurality of first magnetoresistives with a first reference magnetization along a first directional axis. The first bridge circuit includes an output for a first output signal in response to an external magnetic field. The sensor circuit comprises a second bridge circuit. The second bridge circuit (half-bridge or full-bridge) comprises a plurality of second magnetoresistives with a second reference magnetization along a second directional axis. The second bridge circuit includes an output for a second output signal in response to the (same) external magnetic field.The sensor circuit comprises a sensor configured to measure a physical quantity indicating a reference magnetization rotation of the first and second magnetoresistances. This reference magnetization rotation can be due to mechanical stress or other environmental factors. The sensor circuit further comprises a processing circuit arrangement configured to determine a compensated output signal based on the first output signal, the second output signal, and the measured physical quantity indicating the reference magnetization rotation. This compensation aims to correct the effects of the reference magnetization rotation.

[0010] One advantage of this sensor circuit design can be improved accuracy and reliability. By measuring the physical quantity indicating the reference magnetization rotation and using it to compensate for the output signals of the bridge circuits, the sensor can correct errors caused by mechanical stress or other factors that would otherwise lead to inaccurate readings. This compensation can ensure that the sensor provides more precise and stable measurements even under varying environmental conditions, thus improving its performance in applications requiring high accuracy, such as sensors in the automotive industry, industrial equipment, and consumer electronics.

[0011] In some embodiments, the first and second reference magnetizations are orthogonal when no external disturbances (e.g., mechanical stress) act on the sensor circuit. The first reference magnetization refers to the direction of magnetization in the first set of magnetoresistives in the absence of external disturbances. The second reference magnetization refers to the direction of magnetization in the second set of magnetoresistives in the absence of external disturbances. In an ideal, undisturbed state, the first and second reference magnetizations can be at right angles (90 degrees) to each other. Factors such as mechanical stress or other environmental influences can alter / rotate the reference magnetizations. The reference magnetizations can be orthogonal when these disturbances are absent.One advantage of orthogonal reference magnetizations in the absence of external disturbances can be improved sensitivity and accuracy in detecting magnetic fields. Orthogonal magnetizations allow the sensor to better detect and differentiate changes in the magnetic field along different axes. This orthogonal arrangement can maximize the sensor's responsiveness to magnetic field fluctuations. If external disturbances such as mechanical stress are present, they can cause the reference magnetizations to rotate. Knowing that the initial state is orthogonal allows the processing circuitry to more accurately calculate and apply the necessary compensations to correct for stress-induced deviations and ensure that the sensor outputs remain accurate. Orthogonal magnetizations can also help reduce cross-sensitivity between the two axes.Changes in the magnetic field along one axis have only a minimal influence on the sensor reading of the other axis.

[0012] In some embodiments, the first bridge circuit comprises a first Wheatstone bridge consisting of four first magnetoresistive resistors, and the second bridge circuit comprises a second Wheatstone bridge consisting of four second magnetoresistive resistors. A Wheatstone bridge typically comprises four resistors arranged in a diamond shape. It may have two input terminals for a voltage supply and two output terminals where the differential voltage is measured. In this case, the resistors are magnetoresistive resistors, whose resistance changes in response to external magnetic fields. The differential voltage output by the bridge is a measure of the magnetic field. One advantage of using Wheatstone bridge configurations for the first and second bridge circuits can be the high sensitivity and accuracy in detecting small changes in magnetic fields. Wheatstone bridges are sensitive to small changes in resistance.When magnetoresistives undergo changes in external magnetic fields, the corresponding resistance changes can be detected with high precision. The Wheatstone bridge provides a balanced method for measuring resistance changes. It can suppress noise and common-mode signals that could otherwise impair the sensor's accuracy. The bridge's differential output can help measure small changes in resistance, making it suitable for precise magnetic field measurements.

[0013] In some embodiments, the first output signal is a voltage difference between the center nodes of the first bridge circuit, and the second output signal is a voltage difference between the center nodes of the second bridge circuit. In half-bridge configurations, the center node is typically where the two resistors connect to form a single node. The voltage difference can be measured between this center node and a reference point (usually ground or another fixed potential). This provides a simpler, yet effective, measure of the resistance change due to the magnetic field. In full-bridge configurations, the center nodes are the points where the pairs of resistors connect. In a full bridge, there are typically two such nodes. The voltage difference between these two center nodes is taken as the output signal.This differential output provides a measure of the change in resistance due to the external magnetic field.

[0014] In some embodiments, the sensor is configured to measure a mechanical stress acting on the sensor circuit as the physical quantity indicating the (stress-based) reference magnetization rotation. Reference magnetization rotation manifests as a rotation of the reference magnetization direction, which in turn leads to transverse sensitivity to the field orthogonal to the magnetization direction. The mechanical stress acting on the sensor circuit can cause changes in the reference magnetization direction of the magnetoresistives. By measuring this stress, the sensor circuit can determine the extent of the magnetization rotation and apply appropriate compensation to maintain accuracy. The measured physical quantity can be the mechanical stress, indicating how much the reference magnetization has rotated due to external factors such as pressure, temperature changes, or vibrations.There are several ways to measure mechanical stress in a sensor circuit, including strain gauges, piezoresistive sensors, the piezoresistive effect in semiconductor materials, or capacitive sensors. By measuring mechanical stress and understanding its effect on the reference magnetization, the sensor circuit can apply compensations to correct for these effects. This ensures that the output signals remain accurate despite the presence of stress.

[0015] In some embodiments, the sensor is configured to measure the temperature acting on the sensor circuit as the physical quantity indicating the reference magnetization rotation. By measuring the temperature, the sensor can infer the extent of magnetization rotation due to thermal effects and apply compensation to maintain accuracy. Temperature fluctuations can cause thermal expansion or contraction of materials, leading to mechanical stress and, consequently, changes in the reference magnetization direction of magnetoresistives. Measuring the temperature can help determine the degree of magnetization rotation caused by thermal effects. Several methods exist for measuring temperature in a sensor circuit, including thermocouples, thermistors, RTDs (resistance temperature detectors), or semiconductor temperature sensors.

[0016] In some embodiments, the processing circuitry is configured to scale the measured physical quantity by a predetermined scaling factor. This means that the sensor circuitry can include a processing circuitry that adjusts the measured physical quantity (such as voltage or temperature) by multiplying it by a specific scaling factor. This scaling factor, also known as the cross-sensitivity coefficient, can be used to calibrate the effect of the physical quantity on the sensor's reference magnetization rotation. The processing circuitry can take the measured physical quantity (e.g., mechanical stress or temperature) and multiply it by a predetermined scaling factor.This can be the scaling factor used to quantify the relationship between the physical quantity and its effect on the reference magnetization rotation. Essentially, it calibrates the sensor to account for the degree of influence of the measured physical quantity on the sensor's performance. Scaling ensures that the compensation applied to the sensor output is proportional to the actual effect of the measured physical quantity. This can help accurately correct deviations caused by voltage or temperature changes. By using a predetermined scaling factor, the sensor's compensation mechanism can be finely tuned to the specific characteristics of the physical quantity's effect on the reference magnetization.

[0017] In some embodiments, the processing circuitry is configured to determine the compensated output signal based on the difference between the first and second output signals, scaled according to the measured physical quantity. The first output signal is generated by the first bridge circuit in response to the external magnetic field. The second output signal is generated by the second bridge circuit in response to the same external magnetic field. The measured physical quantity could be a measurement of mechanical stress, temperature, or another factor that affects the sensor's reference magnetization and its output signals. The second output signal can be scaled according to the measured physical quantity.This means that the second output signal can be adjusted by a predetermined scaling factor (cross-sensitivity coefficient) based on the measured voltage or temperature. The processing circuitry calculates the difference between the first output signal and the scaled second output signal. This difference, which now incorporates the influence of the measured physical quantity on the second output signal, results in a compensated output signal (e.g., the magnetic field component along the x-axis B). x ), which takes external influences into account. This approach can improve the accuracy and reliability of the sensor by providing precise compensation for environmental influences, resulting in consistent and robust performance.

[0018] In some embodiments, the processing circuit arrangement is configured to determine a first compensated output signal based on a difference between the first output signal and the second output signal, scaled according to the measured physical quantity, and to determine a second compensated output signal based on the sum of the second output signal and the first output signal, scaled according to the measured physical quantity. The first compensated output signal (e.g., the magnetic field component along the x-axis B) x ) can be determined by taking the difference between the first output signal and the second output signal, where the second output signal is scaled based on the measured physical quantity. The second compensated output signal (e.g., the magnetic field component along the y-axis B) yThe value can be determined by taking the sum of the second output signal and the first output signal, where the first output signal is scaled based on the measured physical quantity. This approach can enable independent compensation of the magnetic field components along different axes, leading to more accurate and reliable multi-axis magnetic field measurements.

[0019] In some embodiments, the processing circuit arrangement is configured to determine a first compensated output signal based on the difference between the first output signal, scaled by a first scaling factor based on the squared transverse sensitivity, and the second output signal, scaled by a second scaling factor based on the transverse sensitivity. It also determines a second compensated output signal based on the sum of the second output signal scaled by the first scaling factor and the first output signal scaled by the second scaling factor. This can describe a method for calculating compensated output signals Bx and By that accounts for transverse sensitivity effects in xMR sensors. The first output signal can represent the magnetic field measurement along an axis (e.g., horizontal or B). hor). The second output signal can represent the magnetic field measurement along the orthogonal axis (e.g., vertical or B). vert ) represent. Cross-sensitivity (S cr ) can refer to the undesired influence of the magnetic field of one axis on the measurement of the other axis due to mechanical stress or other factors. To determine the first compensated output signal (Bx), the first output signal (e.g., B) can be hor ) with a factor based on the squared cross-sensitivity, e.g. (1-S cr 2 / 2), can be scaled. The second output signal (e.g., B vert ) can be multiplied by a factor based on the cross-sensitivity S cr can be scaled. The first compensated output signal B x can then be determined by taking the difference between these two scaled signals. To determine the second compensated output signal (By), the second output signal (e.g., B) can be used. vert) with a factor based on the squared cross-sensitivity, e.g. (1-S cr 2 / 2), can be scaled. The first output signal (e.g., B hor ) can be multiplied by a factor based on the cross-sensitivity S cr can be scaled. The first compensated output signal B x The value can then be determined by taking the sum of these two scaled signals. This can lead to precise compensation of cross-sensitivity effects and thus to improved measurement accuracy and reliability.

[0020] In some embodiments, the sensor circuit further includes a third bridge circuit. This third bridge circuit comprises a plurality of third magnetoresistives with the first reference magnetization oriented along the first directional axis. The third bridge circuit includes an output for a third output signal in response to the external magnetic field. The first and third bridge circuits form a differential sensor. The processing circuitry is designed to determine the compensated output signal based on the first to third output signals and the physical quantity indicating the reference magnetization rotation. This describes an enhanced sensor configuration for improved measurement accuracy and compensation. The first and third bridge circuits can be used together to form a differential sensor.A differential sensor uses two measurements (from the first and third bridge circuits) to improve the accuracy and robustness of the output signal by suppressing common-mode noise and errors. By employing a differential sensor configuration (first and third bridge circuits), the sensor can suppress common-mode noise and environmental disturbances that affect both circuits equally. This can lead to more accurate and reliable measurements. The processing circuitry combines the output signals from all three bridge circuits (first, second, and third) and uses the measured physical quantity (indicating the reference magnetization rotation, such as mechanical stress or temperature) to determine a compensated output signal.The compensated output signal is calculated using the first, second, and third output signals, adjusted based on the measured physical quantity indicating the extent of the reference magnetization rotation. This configuration can improve measurement accuracy and noise suppression, ensuring reliable and precise sensor performance under various environmental conditions.

[0021] In some embodiments, the processing circuitry is designed to determine the compensated output signal based on the difference between the first and third output signals and the second output signal, scaled according to the measured physical quantity. This means that the sensor circuit comprises three bridge circuits. The first bridge circuit includes magnetoresistives with a reference magnetization along the first directional axis and outputs the first signal in response to the external magnetic field. The second bridge circuit includes magnetoresistives with a reference magnetization along a second (typically orthogonal) directional axis and outputs the second signal in response to the external magnetic field.The third bridge circuit comprises magnetoresistives with a reference magnetization along the first directional axis, similar to the first bridge circuit, and outputs the third signal in response to the external magnetic field. The processing circuitry calculates the difference between the first and third output signals. This difference helps reduce common-mode noise and errors, thus improving measurement accuracy. The second output signal is scaled based on the measured physical quantity (such as voltage or temperature) to compensate for the influence of this quantity on the sensor's reference magnetization. The compensated output signal can be derived by combining the difference signal (the difference between the first and third output signals) and the scaled second output signal.This method ensures that the compensation takes the measured physical quantity into account, resulting in a more accurate and reliable sensor output. An advantage of this approach is improved compensation for environmental influences and higher accuracy. By using the difference between the first and third output signals, the sensor can effectively suppress common-mode noise and environmental disturbances that affect both circuits equally. This can lead to more accurate and stable measurements. Scaling the second output signal based on the measured physical quantity allows for precise compensation of errors due to mechanical stress, temperature fluctuations, or other environmental factors, ensuring that the sensor output remains accurate under varying conditions.

[0022] In some embodiments, the magnetoresistive devices are tunnel magnetoresistive devices (TMRs). TMRs utilize the tunnel magnetoresistance effect, which occurs when electrons tunnel through an insulating barrier between two ferromagnetic layers, with the resistance changing depending on the relative orientation of the magnetization in these layers. TMRs comprise two ferromagnetic layers separated by a thin insulating barrier. When a voltage is applied, electrons tunnel through the insulating barrier, and the resistance of the device changes depending on whether the magnetizations of the ferromagnetic layers are parallel or antiparallel. The resistance is lower when the magnetizations are parallel and higher when they are antiparallel. An advantage of using TMRs is their high sensitivity and large magnetoresistance ratio.TMR resistors typically exhibit a much higher magnetoresistance ratio than other types of magnetoresistance, such as anisotropic magnetoresistance (AMR) or giant magnetoresistance (GMR). This means they can detect smaller changes in magnetic fields with greater precision. The high sensitivity of TMR resistors enables more accurate detection of magnetic fields, which is crucial for applications requiring precise measurements, such as hard disk drives, magnetic field sensors, and various types of sensor applications in the automotive and industrial sectors.

[0023] In some embodiments, the sensor circuit is an integrated circuit. This means that the sensor circuit, which includes the magnetoresistives and the processing circuitry, can be manufactured as a single integrated circuit (IC) instead of consisting of separate, discrete components. An integrated circuit is a set of electronic components, such as resistors, capacitors, transistors, and other devices, all fabricated on a single piece of semiconductor material, typically silicon. This allows for the creation of compact, efficient, and high-performance electronic systems.

[0024] According to another aspect, the present disclosure provides a method for compensating mechanical stress on a magnetoresistive sensor. The method comprises receiving a first output signal from one or more first magnetoresistives with a first reference magnetization along a first directional axis (e.g., x-axis) in response to an external magnetic field. The method comprises receiving a second output signal from one or more second magnetoresistives with a second reference magnetization along a second directional axis (e.g., y-axis) in response to the external magnetic field. The method includes receiving an additional sensor signal indicating a reference magnetization rotation of the first and second magnetoresistives.The procedure further includes determining a compensated output signal based on the first output signal, the second output signal and the additional sensor signal.

[0025] In some embodiments, the method includes determining the compensated output signal based on a difference between the first output signal and the second output signal, scaled based on the additional sensor signal.

[0026] In some embodiments, the method includes determining a first compensated output signal based on a difference between the first output signal and the second output signal, scaled on the basis of the additional sensor signal, and determining a second compensated output signal based on a sum of the second output signal and the first output signal, scaled on the basis of the additional sensor signal.

[0027] In some embodiments, the method comprises determining a first compensated output signal based on a difference between the first output signal, scaled by a first scaling factor based on the squared cross-sensitivity, and the second output signal, scaled by a second scaling factor based on the cross-sensitivity, and determining a second compensated output signal based on a sum of the second output signal, scaled by the first scaling factor, and the first output signal, scaled by the second scaling factor.

[0028] According to another aspect, the present disclosure provides a computer program comprising a sequence of instructions, wherein, when executed by a processor, the instructions cause the processor to execute the procedure from any of the previous examples.

[0029] The present disclosure proposes a scheme to locally suppress both xMR voltage effects by compensating for the sensitivity loss and the reference angle rotation with a linear compensation that can be implemented in an analog or digital circuit arrangement. The shear voltage can be measured directly with a rotated current mirror or indirectly via its strong temperature dependence. Brief description of the characters

[0030] The following are some examples of devices and / or methods, described solely by way of example and with reference to the accompanying figures, in which the following applies: Fig. Figure 1 shows a schematic representation of a layer stack of a magnetoresistive sensor element; Fig. Figure 2 shows a relationship between cross-sensitivity and reference system rotation in a magnetic sensor system; Fig. 3A shows a sensor circuit according to an embodiment of the present disclosure; Fig. 3B shows a sensor circuit according to a further embodiment of the present disclosure; Fig. 4 shows a differential sensor circuit according to an embodiment of the present disclosure; Fig. 5A shows a differential sensor circuit according to a further embodiment of the present disclosure; Fig. 5B shows a differential sensor circuit according to a further embodiment of the present disclosure; Fig. Figure 5C shows an alternative setup for the second bridge circuit; Fig. Figure 6 shows an angle sensor circuit with first-order compensation according to an embodiment of the present disclosure; and Fig. Figure 7 shows an angle sensor circuit with second-order compensation according to an embodiment of the present disclosure. Detailed description

[0031] Some examples are now described in more detail with reference to the accompanying figures. However, other possible examples are not limited to the features of these detailed embodiments. Other examples may exhibit modifications of the features, as well as equivalents and alternatives to the features. Furthermore, the terminology used herein to describe certain examples should not be considered restrictive for other possible examples.

[0032] Identical or similar reference symbols throughout the description of the figures refer to identical or similar elements and / or features, which may be implemented identically or in a modified form, while providing the same or a similar function. Furthermore, the thickness of lines, layers, and / or areas in the figures may be exaggerated for clarity.

[0033] When two elements A and B are combined using "or," this is to be understood as revealing all possible combinations, i.e., only A, only B, and A and B, unless explicitly defined otherwise in a specific case. As an alternative formulation for the same combinations, "at least one of A and B" or "A and / or B" can be used. This applies accordingly to combinations of more than two elements.

[0034] When a singular form, e.g., "ein, eine" and "der, die, das", is used, and the use of only a single element is neither explicitly nor implicitly defined as mandatory, subsequent examples may also use multiple elements to implement the same function. If a function is subsequently described as being implemented using multiple elements, further examples may implement the same function using a single element or a single processing entity.It is further understood that the terms "include", "comprehensive", "exhibit" and / or "exhibit" when used describe the presence of the specified features, integers, steps, operations, processes, elements, components and / or a group thereof, but do not exclude the presence or addition of one or more other features, integers, steps, operations, processes, elements, components and / or a group thereof.

[0035] Fig. Figure 1 shows an example of a layer stack of a magnetoresistive sensor element 100 according to one or more embodiments.

[0036] The magnetoresistive sensor element 100 can, for example, be a TMR sensor element with a bottom-pinned spin-valve (BSV) configuration. GMR sensor elements are also possible. The magnetoresistive sensor element 100 can be arranged on a semiconductor substrate (not shown) of a magnetoresistive sensor. When described using a Cartesian coordinate system with mutually perpendicular coordinate axes x, y, and z, the layers of the stack extend laterally in an xy-plane spanned by the x and y axes. Thus, lateral dimensions (e.g., lateral distances, lateral cross-sectional areas, lateral surfaces, lateral extents, lateral displacements, etc.) can refer to dimensions in the xy-plane, and vertical dimensions can refer to dimensions in the z-direction, perpendicular to the xy-plane.For example, the vertical extent of a layer in the z-direction can be referred to as the layer thickness.

[0037] The layer stack of the magnetoresistive sensor element 100 comprises at least one reference layer with a reference magnetization (e.g., a reference direction in the case of GMR or TMR technology). The reference magnetization is a magnetization direction that provides a sensor direction corresponding to a sensor axis of the magnetoresistive sensor element 100. The reference layer, and thus the reference magnetization, defines a sensor plane. The sensor plane can be defined, for example, by the xy-plane. Therefore, the x-direction and the y-direction can be described as "in-plane" with respect to the sensor plane, while the z-direction can be described as "out-of-plane" with respect to the sensor plane.

[0038] Accordingly, in the case of a GMR or TMR sensor element, the resistance of the magnetoresistive sensor element 100 is minimal when the free magnetization of a magnetic free layer points in exactly the same direction as the reference magnetization (e.g., the reference direction), and the resistance of the magnetoresistive sensor element 100 is maximal when the free magnetization of the magnetic free layer points in exactly the opposite direction to the reference magnetization. The orientation of the free magnetization of the magnetic free layer is variable in the presence of an external magnetic field. Thus, the resistance of the magnetoresistive sensor element 100 can vary based on the influence of the external magnetic field on the free magnetization of the free layer.

[0039] From bottom to top, the magnetoresistive sensor element 100 can include an optional seed layer 102, which can be used to influence and / or optimize stack growth. In some embodiments, the seed layer 102 can comprise copper (Cu), tantalum (Ta), ruthenium (Ru), or a combination thereof. In the example shown, a natural antiferromagnetic (NAF) layer 104 is formed or otherwise arranged on the seed layer 102. The NAF layer 104 can comprise platinum-manganese (PtMn), iridium-manganese (IrMn), nickel-manganese (NiMn), or the like. The thickness of the NAF can range, for example, from 5 nm to 50 nm.

[0040] Furthermore, a pinned layer (PL) 106 can be formed or otherwise arranged on the NAF layer 104. The pinned layer 106 can comprise a ferromagnetic material, e.g., cobalt-iron (CoFe) or cobalt-iron-boron (CoFeB). Contact between the NAF layer 104 and the pinned layer 106 can induce an effect known as the exchange bias effect, which causes the magnetization of the pinned layer 106 to align in a preferred direction (e.g., in the x-direction, as shown). The magnetization of the pinned layer 106 can be referred to as pinned magnetization. The pinned layer 106 can exhibit a linear magnetization pattern in the xy-plane (e.g., a homogeneous alignment in one direction) that is permanently fixed.

[0041] The magnetoresistive sensor element 100 also includes a non-magnetic layer (NML), referred to as a coupling layer 108. In one possible embodiment, the coupling layer 108 can comprise ruthenium (Ru), iridium (Ir), copper (Cu), copper alloys, or similar materials. Other materials (e.g., paramagnets) are also possible. A magnetic (e.g., ferromagnetic) reference layer (RL) 110 can be formed on the coupling layer 108 or arranged otherwise. The thickness of the pinned layer 106 and the magnetic reference layer 110 can, for example, range from 1 nm to 10 nm.

[0042] Accordingly, the coupling intermediate layer 108 can be arranged between the pinned layer 106 and the magnetic reference layer 110 to spatially separate the pinned layer 106 and the magnetic reference layer 110 in the vertical direction. Furthermore, the coupling intermediate layer 108 can provide an interlayer exchange coupling (e.g., an antiferromagnetic Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling) between the pinned layer 106 and the magnetic reference layer 110 to form an artificial antiferromagnet. Consequently, the magnetization of the magnetic reference layer 110 can align and be held in a direction that is antiparallel or opposite to the magnetization of the pinned layer 106 (e.g., in the x-direction, as shown). The magnetization of the magnetic reference layer 110 can be referred to as the reference magnetization.

[0043] Since the NAF layer 104 is configured to align and fix the magnetization of the pinned layer 106 in a specific direction, and the coupling intermediate layer 108 is configured to align and fix the magnetization of the magnetic reference layer 110 in an opposite direction, it can be said that the NAF layer 104 is configured to hold the magnetization of the pinned layer 106 (e.g., a fixed magnetization) in a first magnetic orientation and to hold the magnetization of the magnetic reference layer 110 (e.g., a fixed reference magnetization) in a second magnetic orientation. The magnetic reference layer 110 can have a linear magnetization pattern in a specific direction in the xy-plane if the pinned layer 106 has a linear magnetization pattern in an antiparallel direction.Thus, the NAF layer 104, the pinned layer 106, the coupling intermediate layer 108 and the magnetic reference layer 110 form a magnetic reference layer system 112 of the magnetoresistive sensor element 100.

[0044] The magnetoresistive sensor element 100 additionally comprises a barrier layer 114 (e.g., a tunnel barrier) arranged vertically between the reference layer system 112 and a free magnetic layer 116. The barrier layer 114 can, for example, be formed on the magnetic reference layer 110 of the reference layer system 112 or arranged otherwise, and the free magnetic layer 116 can be formed on the barrier layer 114 or arranged otherwise.

[0045] The barrier layer 114 can comprise a non-magnetic material. In some embodiments, the barrier layer 114 can be an electrically insulating tunnel barrier layer. For example, the barrier layer 114 can be a tunnel barrier layer used to generate a TMR effect. The barrier layer 114 can comprise magnesium oxide (MgO) or another material with similar properties.

[0046] The material of the free magnetic layer 116 can be an alloy of a ferromagnetic material, such as CoFe, CoFeB, or NiFe. The free magnetic layer 116 exhibits a free magnetization that is variable in the presence of an external magnetic field. Therefore, the free magnetic layer 116 can be referred to as a sensor layer, since changes in the free magnetization can be used to determine a measured quantity. Furthermore, the free magnetization in the ground state exhibits a standard magnetic orientation (such as vortex magnetization). The ground state is a state in which the influence of the external magnetic field on the free magnetic layer 116 is either non-existent or negligibly small. In some embodiments, the magnetoresistive sensor element 100 can comprise a free magnetic system consisting of a plurality of layers (e.g.,The free magnetic system comprises two or more free magnetic layers that together act as the free magnetic layer. In this case, the free magnetic layers of the free magnetic system are magnetically coupled to each other. Thus, the free magnetic system can function as a single free magnetic layer, but it can also comprise multiple layers. The free magnetic layer exhibits a free magnetization, which is variable in the presence of an external magnetic field.

[0047] A cover layer 118, e.g. tantalum (Ta), tantalum nitride (TaN), ruthenium (Ru), titanium (Ti), titanium nitride (TiN), platinum (Pt) or the like, can be formed on the free magnetic layer 116 or otherwise arranged to form an upper layer of the magnetoresistive sensor element 100.

[0048] The seed layer 102 can serve as a lower electrode or can establish electrical contact with a lower electrode (not shown) of the magnetoresistive sensor element 100. The cover layer 118 can establish electrical contact with an upper electrode (not shown) of the magnetoresistive sensor element 100. The barrier layer 114 can be designed such that electrons can tunnel between the reference layer system 112 and the free magnetic layer 116 when a bias voltage is applied to the electrodes of the magnetoresistive sensor element 100 (not shown) to generate a magnetoresistive effect (e.g., a TMR effect).

[0049] As already mentioned, it serves Fig. 1 merely as an example of a magnetoresistive sensor element or magnetoresistive. Other examples can be found in the description in Fig. 1 differ. The number and arrangement of the in Fig. The components shown in Figure 1A are an example. In practice, the magnetoresistive device can comprise 100 additional elements or layers.

[0050] Mechanical stress can rotate the reference magnetization of the magnetic reference layer 110 or the reference layer system 112 relative to its orientation in the stress-free state. Mechanical stress can influence the magnetic properties of materials due to magnetoelastic coupling, i.e., the interaction between a material's magnetic and elastic properties. When a magnetic material is subjected to mechanical stress, this stress can cause changes in the material's magnetic anisotropy, resulting in a rotation of the reference magnetization direction. Magnetoelastic coupling is the interaction between a material's magnetic and mechanical properties. Stress can alter the material's magnetic energy landscape, leading to changes in the direction of the reference magnetization. Mechanical stress can create or modify anisotropy in the material.Anisotropy refers to the directional dependence of a material's magnetic properties. Stress can either amplify or reorient existing anisotropy, leading to a rotation of the reference magnetization. In TMR sensors or other magnetoresistive sensors, any rotation of the reference magnetization due to mechanical stress can cause errors in the sensor output, as the sensor relies on a stable and precisely defined magnetization direction for accurate measurements.

[0051] Fig. 2 shows a relationship between cross-sensitivity S cr and reference system rotation θ in a magnetic sensor system. The x-axis in Fig. 2 represents the cross-sensitivity S cr in percent (%). The y-axis in Fig. Equation 2 represents the reference system rotation θ in degrees (°). Scr=sin θBhomcos θ Bhom=tan θ shows that the cross-sensitivity S cris essentially equal to the tangent of the angle θ of the reference system rotation or the reference magnetization rotation. The diagonal line in graph 200 shows a direct proportional relationship between the transverse sensitivity S cr and the reference magnetization rotation θ. With increasing reference system / magnetization rotation θ, the cross-sensitivity S also increases. cr A transverse sensitivity of approximately 20% corresponds, for example, to a reference system / magnetization rotation of approximately 11°.

[0052] The inserted diagram in the lower right corner of Fig. Figure 2 visually represents the rotation of the reference system by the rotation angle θ. While the original axes (x and y) represent the original reference (coordinate) system, the axes (x' and y') represent the rotated reference system, e.g., due to mechanical stress.

[0053] A rotated reference system can cause a misalignment between the actual magnetic field direction and the direction perceived by the sensor. This misalignment can lead to errors in the measurement of magnetic field components. The sensor may misinterpret the magnitude and direction of the magnetic field, resulting in inaccurate readings. When the reference system rotates, the sensor becomes more sensitive to magnetic fields in directions to which it was originally less sensitive (increased cross-sensitivity). This increased cross-sensitivity can lead to noise and errors in measurements, especially with multi-axis sensors. Furthermore, rotation can cause interference between the orthogonal axes (e.g., x- and y-axes), making accurate isolation of the magnetic field components more difficult.

[0054] In the present disclosure, compensation concepts are proposed that take the rotated reference system into account and can contribute to correcting the measured values. The proposed compensation concepts can, for example, utilize a known relationship between transverse sensitivity and reference angle rotation (see, e.g., Fig. 2) to adjust the measured values.

[0055] Fig. Figure 3A shows a sensor circuit 300 according to an embodiment of the present disclosure.

[0056] The sensor circuit 300 comprises a first bridge circuit 310. The first bridge circuit 310 comprises a plurality of first magnetoresistive resistors 312 with a first reference magnetization along a first directional axis (here: x-axis). The first bridge circuit 310 also includes an output 314 for a first output signal V. sensas a reaction to an external magnetic field. In the example shown, the first bridge circuit 310 is implemented as a Wheatstone bridge with four first magnetoresistives 312. Ideally (e.g., without voltage), the reference magnetization of the magnetoresistives 312 of the left arm points in the negative x-direction. Ideally, the reference magnetization of the magnetoresistives 312 of the right arm points in the positive x-direction (i.e., 180° offset from the left arm). The first bridge circuit 310 can optionally include an offset trim component to compensate for any inherent offsets in the sensor output V. sens to correct and ensure that the output V sens The magnetic field is centered precisely at zero when no external magnetic field is present. In the example shown, the first bridge circuit 310 is configured to measure an x-component of an external magnetic field and produces an output voltage V. sens The output voltage V sensThis can be a voltage difference between the center nodes of the left and right legs of the first bridge circuit 310. The person skilled in the art, benefiting from the present disclosure, will understand that the first bridge circuit 310 could also be implemented as a half-bridge.

[0057] The first bridge circuit 310 comprises an upper left magnetoresistance 312, a lower left magnetoresistance 312, an upper right magnetoresistance 312, and a lower right magnetoresistance 312. The reference magnetization of the upper left magnetoresistance 312 and the lower left magnetoresistance 312 points in the negative x-direction. The reference magnetization of the upper right magnetoresistance 312 and the lower right magnetoresistance 312 points in the positive x-direction. The upper left magnetoresistance 312 and the lower right magnetoresistance 312 are connected in series between the supply potential and ground (first series connection). The upper right magnetoresistance 312 and the lower left magnetoresistance 312 are connected in series between the supply potential and ground (second series connection). The output voltage V senscan be a voltage difference between the center node of the first series circuit and the second series circuit of the first bridge circuit 310.

[0058] The sensor circuit 300 additionally comprises a second bridge circuit 320. The second bridge circuit 320 comprises a plurality of second magnetoresistives 322 with a second reference magnetization along a second directional axis (here: y-axis). The second bridge circuit 320 also includes an output 324 for a second output signal V. orthoas a reaction to the external magnetic field. In the example shown, the second bridge circuit 320 is implemented as a Wheatstone bridge with four first magnetoresistives 322. Ideally (e.g., without voltage), the reference magnetization of the magnetoresistives 322 of the left arm points in the positive y-direction. Ideally, the reference magnetization of the magnetoresistives 322 of the right arm points in the negative y-direction (i.e., offset by 180° relative to the left arm). The second bridge circuit 320 can optionally include an offset trim component to compensate for any inherent offsets in the sensor output V. ortho to correct and ensure that the output V ortho The magnetic field is centered precisely at zero when no external magnetic field is present. In the example shown, the second bridge circuit 320 is configured to measure a y-component of the external magnetic field and produces an output voltage V. ortho The output voltage V orthoThis can be a voltage difference between the center nodes of the left and right legs of the second bridge circuit 320. The person skilled in the art, benefiting from the present disclosure, will understand that the second bridge circuit 320 could also be implemented as a half-bridge.

[0059] The second bridge circuit 320 comprises an upper left magnetoresistance 322, a lower left magnetoresistance 322, an upper right magnetoresistance 322, and a lower right magnetoresistance 322. The reference magnetization of the upper left magnetoresistance 322 and the lower left magnetoresistance 322 points in the positive y-direction. The reference magnetization of the upper right magnetoresistance 322 and the lower right magnetoresistance 322 points in the negative y-direction. The upper left magnetoresistance 322 and the lower right magnetoresistance 322 are connected in series between the supply potential and ground (first series connection). The upper right magnetoresistance 322 and the lower left magnetoresistance 322 are connected in series between the supply potential and ground (second series connection). The output voltage V orthoThe voltage difference between the center node of the first series circuit and the second series circuit of the second bridge circuit can be 320.

[0060] The sensor circuit 300 further comprises a sensor 330 configured to measure a physical quantity 334 indicating a reference system / magnetization rotation θ of the first magnetoresistances 312 and the second magnetoresistances 322. The physical quantity 334 measured by the sensor 330 can be mechanical stress, temperature, or any other factor that influences the orientation of the reference magnetization in the magnetoresistances 312 and 322. The measured physical quantity can help determine the extent to which the reference system / magnetization has rotated due to external influences.

[0061] In some embodiments, all components of the sensor circuit 300 can be implemented on a common substrate, e.g., on a common semiconductor substrate (die). That is, the sensor circuit 300 can be an integrated sensor circuit (sensor IC).

[0062] In an implementation ( Fig. 3A) The sensor 330 can be configured to measure the mechanical (shear) stress acting on the sensor circuit 300 as the physical quantity that indicates a reference magnetization change, which manifests itself as a rotation θ of the reference magnetization direction, which in turn leads to a cross-sensitivity S cr leads orthogonally to the direction of magnetization relative to the field.

[0063] Mechanical stress can be measured using various techniques and specialized circuit arrangements designed for stress detection and quantification. The piezoresistive effect, for example, utilizes the change in a material's resistance under mechanical stress. The resistance of a single-color resistive strip changes depending on the applied voltage, which can be measured and used to quantify the stress. In the piezo-MOS effect, mechanical stress alters the mobility of charge carriers in the channels of MOSFETs, affecting the current gain and threshold voltage. These changes can be measured to determine the stress voltage. The piezo-junction effect involves changes in the mobility of minority carriers in the base of a bipolar transistor and changes in the intrinsic carrier density, which affect the saturation current.The voltage can be measured by observing these changes. In the piezoelectric Hall effect, mechanical stress alters the Hall coefficient, thereby changing the current-related magnetic sensitivity of Hall plates. Measuring these changes in Hall sensitivity can indicate the voltage level.

[0064] The Sensor 330, for example, can incorporate MOS current mirrors with orthogonal current flow directions, which can serve as voltage-sensitive elements. An advantage is that the signal is in the current domain, which simplifies multiplexing an array of elements to a single terminal. A combination of low-n doped lateral resistors in an L-layout (lateral resistors) and low-n doped vertical resistors (vertical resistors) can be used for voltage measurement. The difference in their resistance changes under voltage can be used to quantify the voltage. Four resistors in an L-layout can form a Wheatstone bridge circuit. The output voltage of the bridge is proportional to the difference of the in-the-plane normal voltage components (o xx -σ yy ) and enables a measurement of the voltage.

[0065] In another implementation of the sensor circuit 300 ( Fig. 3B) The sensor 330 can be configured to measure the temperature acting on the sensor circuit 300 as the physical quantity that indicates the mechanical (shear) stress and thus the reference magnetization rotation. By measuring the temperature, the sensor 330 can infer the extent of the magnetization rotation due to thermal effects and apply compensation to maintain accuracy. Temperature fluctuations can cause thermal expansion or contraction of materials, leading to mechanical stress and, consequently, changes in the reference magnetization direction of magnetoresistives. Measuring the temperature can help determine how much the magnetization has rotated due to thermal effects. There are several methods for measuring the temperature in a sensor circuit, including thermocouples, thermistors, RTDs (resistance temperature detectors), or semiconductor temperature sensors.Voltage measurement can therefore also be achieved through temperature measurement and a conversion such as S. cr (T) = (T-150) / (190)*0.2 can be replaced, which is obtained, for example, from measurement data. The remaining transverse sensitivity is expected to be at the level of approximately ±3%, and it can be further reduced by fine-tuning the sample at 150°: S cr (T) = (T-150) / (190)*0.2+trim.

[0066] Temperature and / or voltage sensors can be placed near the circuit elements 310, 320 to measure the temperature and / or voltage acting on the circuit elements 310, 320 and to provide inputs for compensation circuits that correct voltage-related deviations.

[0067] The sensor circuit 300 further comprises a processing circuit arrangement (compensation circuit) 340, which is configured to generate a compensated output signal 344 based on the first output signal V sens, of the second output signal V ortho and the physical quantity 334, which indicates the reference system / magnetization rotation θ. The compensation can be based on the following relationship: [BxBy]=[cos θ−sin θsin θcos θ][BsensBortho], where B sens corresponds to the first output signal, B ortho corresponds to the second output signal, B x corresponds to a compensated first output signal and B y corresponds to a compensated second output signal.

[0068] That is, based on the first and second output signals B sens and B ortho can the compensated first output signal B x to be determined according to Bx=Bsenscos θ−Borthosin θ,Bx≈Bsens−Bortho θ=Bsens−Bortho tan(Scr)Bx≈Bsens−BorthoScr,Bx≈Bsens−Borthoσxyccr.

[0069] This equation represents a linear approximation, where B xThe compensated magnetic field component in the x-direction. It can be calculated by the product of the orthogonal voltage output B. ortho and the cross-sensitivity S cr from the primary voltage output B sens is subtracted.

[0070] Based on the first and second output signals B sens and B ortho can the compensated second output signal B y to be determined according to By=Bsenssin θ+Borthocos θ,By≈Bsensθ+Bortho=Bsenstan(Scr)+Bortho,By≈BsensScr+Bortho,By≈Bsensσxyccr+Bortho.

[0071] This equation represents a linear approximation, where B y The compensated magnetic field component in the y-direction is calculated by summing the voltage output B. sens multiplied by the transverse sensitivity S cr and the orthogonal voltage output B ortho will be calculated.

[0072] Here, θ denotes atan (Scr ) the reference magnetization rotation, S cr = σ xy c cr refers to the cross-sensitivity, and c cr = e.g. 0.3% / MPa denotes the transverse sensitivity coefficient. The shear stress σ xy It can be measured or trimmed, for example, using a temperature-dependent LUT value. The processing circuit arrangement 340 can thus be configured to measure the physical quantity that is the (shear) stress σ. xy indicates, through a predetermined scaling factor c cr(Transverse sensitivity coefficient) to scale further. The transverse sensitivity coefficient is material-dependent. The transverse sensitivity coefficient refers to how sensitive a sensor or material is to unintended stimuli, such as mechanical stress, which can lead to deviations in the sensor's intended measurements. Different materials can exhibit varying stiffness, which affects their deformation under stress. Materials with a higher modulus of elasticity generally exhibit less deformation, which affects transverse sensitivity. Materials such as silicon exhibit piezoresistive effects, where mechanical stress changes the electrical resistance. The magnitude of this effect varies with the material's properties. The atomic arrangement within the material can affect how stress propagates through it.Single-crystal silicon, for example, exhibits anisotropic properties, meaning its response to stress varies with the direction of the stress. In silicon, the level and type of doping (n-type or p-type) can influence the piezoresistive coefficients. Heavily doped silicon may exhibit a different stress sensitivity compared to lightly doped silicon. The temperature dependence of piezoresistive effects means that the cross-sensitivity can vary with temperature. This dependence is material-specific and requires calibration for accurate compensation. Therefore, the cross-sensitivity coefficient depends on the material and is influenced by its intrinsic properties, doping levels, temperature effects, and manufacturing processes.

[0073] The processing circuit arrangement 340 of Fig. 3A or Fig. 3B can be trained to compensate the output signal B xbased on a difference between the first output signal B sens and the second output signal B ortho, scaled based on the measured physical quantity, e.g. scaled by S cr = σ xy c cr , to determine. Additionally or alternatively, the processing circuit arrangement 340 can be configured to determine the compensated output signal B. y based on a sum of the second output signal B ortho and the first output signal B sens , scaled based on the measured physical quantity 334, e.g. scaled by S cr = σ xy c cr , to determine. The material-specific scaling factor c cr (e.g. 0.24% / MPa) can be used to quantify the sensor's sensitivity to mechanical stress (σ). xy). 0.24% / MPa means that the parameter in question (e.g., the output voltage) changes by 0.24 percent for every megapascal (MPa) of the applied voltage.

[0074] Fig. Figure 4 shows a sensor circuit 400 according to another embodiment of the present disclosure. Here, the external magnetic field component B can be x can be determined differentially. A differential measurement of the external magnetic field component B x This involves comparing the magnetic field detected by two or more sensors to measure the difference between their outputs. This technique can help improve the accuracy and sensitivity of the measurement by reducing the influence of common-mode noise and other external disturbances. In differential measurement, two magnetic sensors are placed in close proximity but separated by a small distance. These sensors detect the magnetic field component B. xat their respective locations. The outputs of the two sensors are compared to find the difference between them. This differential output effectively measures the change in the magnetic field over the distance between the sensors.

[0075] The differential sensor circuit 400 comprises a first left-hand bridge circuit 310-L. The first left-hand bridge circuit 310-L comprises a plurality of first magnetoresistive resistors 312 with a first reference magnetization along a first directional axis (here: x-axis). The first left-hand bridge circuit 310-L also includes an output for a first left-hand output signal V. sens,leftin response to an external magnetic field. In the example shown, the first left bridge circuit 310-L is implemented as a Wheatstone bridge with four first magnetoresistives 312. Ideally (e.g., without voltage), the reference magnetization of the magnetoresistives 312 of the left arm points in the negative x-direction. Ideally, the reference magnetization of the magnetoresistives 312 of the right arm points in the positive x-direction. The first left bridge circuit 310-L can optionally include an offset trim component to correct any inherent offsets in the sensor output and to ensure that the output is precisely centered around zero when no external magnetic field is present. In the example shown, the first left bridge circuit 310-L is configured to measure an x-component of an external magnetic field and produces an output voltage V. sens,left The output voltage V sens,leftThis can be a voltage difference between the center nodes of the left and right legs of the first left-hand bridge circuit 310-L. The person skilled in the art, benefiting from the present disclosure, will understand that the first left-hand bridge circuit 310-L could also be implemented as a half-bridge.

[0076] The differential sensor circuit 400 additionally includes a second left-hand bridge circuit 320-L. This second left-hand bridge circuit 320-L comprises a plurality of second magnetoresistives 322 with a second reference magnetization along a second directional axis (here: y-axis). The second left-hand bridge circuit 320-L also includes an output for a second output signal V. ortho,leftin response to the external magnetic field. In the example shown, the second left-hand bridge circuit 320-L is implemented as a Wheatstone bridge with four first magnetoresistives 322. Ideally (e.g., without voltage), the reference magnetization of the magnetoresistives 322 of the left arm points in the positive y-direction. Ideally, the reference magnetization of the magnetoresistives 322 of the right arm points in the negative y-direction. The second left-hand bridge circuit 320-L can optionally include an offset trim component to correct any inherent offsets in the sensor output and to ensure that the output is precisely centered around zero when no external magnetic field is present. In the example shown, the second left-hand bridge circuit 320-L is configured to measure a y-component of the external magnetic field and produces an output voltage V. ortho,left The output voltage V ortho,leftThis can be a voltage difference between the center nodes of the left and right legs of the second left bridge circuit 320-L. The person skilled in the art, benefiting from the present disclosure, will understand that the second bridge circuit 320 could also be implemented as a half-bridge.

[0077] The differential sensor circuit 400 further comprises a left sensor 330-L configured to measure a physical quantity 334 indicating a reference magnetization rotation θ of the first left magnetoresistives 312 and the second left magnetoresistives 322. The physical quantity 334 measured by the sensor 330 can be mechanical stress, temperature, or any other factor that influences the orientation of the reference magnetization in the magnetoresistives 312 and 322.

[0078] The differential sensor circuit 400 also includes a first right-hand bridge circuit 310-R, which is located in close proximity to, but separated by a small distance from, the first left-hand bridge circuit 310-L. The first right-hand bridge circuit 310-R comprises a plurality of first magnetoresistive resistors 312 with a first reference magnetization along a first directional axis (here: x-axis). The first right-hand bridge circuit 310-R also includes an output for a first right-hand output signal V. sens,rightin response to the external magnetic field. In the example shown, the first right-hand bridge circuit 310-R is implemented as a Wheatstone bridge with four first magnetoresistives 312. Ideally (e.g., without voltage), the reference magnetization of the magnetoresistives 312 of the left arm points in the negative x-direction. Ideally, the reference magnetization of the magnetoresistives 312 of the right arm points in the positive x-direction. The first right-hand bridge circuit 310-R can optionally include an offset trim component to correct any inherent offsets in the sensor output and to ensure that the output is precisely centered around zero when no external magnetic field is present. In the example shown, the first right-hand bridge circuit 310-R is configured to measure an x-component of an external magnetic field and produces an output voltage V. sens,right The output voltage V sens,rightThis can be a voltage difference between the center nodes of the left and right legs of the first right-hand bridge circuit 310-R. The person skilled in the art, benefiting from the present disclosure, will understand that the first right-hand bridge circuit 310-R could also be implemented as a half-bridge.

[0079] The differential sensor circuit 400 additionally includes a second right-hand bridge circuit 320-R, which is located in close proximity to, but separated by a small distance from, the second left-hand bridge circuit 320-L. The second right-hand bridge circuit 320-R comprises a plurality of second magnetoresistives 322 with a second reference magnetization along a second directional axis (here: y-axis). The second right-hand bridge circuit 320-R also includes an output for a second right-hand output signal V. or- tho,rightin response to the external magnetic field. In the example shown, the second right-hand bridge circuit 320-R is implemented as a Wheatstone bridge with four first magnetoresistives 322. Ideally (e.g., without voltage), the reference magnetization of the magnetoresistives 322 of the left arm points in the positive y-direction. Ideally, the reference magnetization of the magnetoresistives 322 of the right arm points in the negative y-direction. The second right-hand bridge circuit 320-R can optionally include an offset trim component to correct any inherent offsets in the sensor output and to ensure that the output is precisely centered around zero when no external magnetic field is present. In the example shown, the second right-hand bridge circuit 320-R is configured to measure a y-component of the external magnetic field and produces an output voltage V. ortho,right The output voltage V ortho,rightThis can be a voltage difference between the center nodes of the left and right legs of the second right-hand bridge circuit 320-R. The person skilled in the art, benefiting from the present disclosure, will understand that the second bridge circuit 320 could also be implemented as a half-bridge.

[0080] The differential sensor circuit 400 further comprises a right-hand sensor 330-R configured to measure the physical quantity indicating a reference magnetization rotation θ of the first right-hand magnetoresistives 312 and the second right-hand magnetoresistives 322. The physical quantity measured by the sensor 330-R can be mechanical stress, temperature, or any other factor that influences the orientation of the reference magnetization in the magnetoresistives.

[0081] The processing circuit arrangement 340 of the differential sensor circuit 400 can be configured to generate the compensated left output signal according to Bx,left≈Bsens,left−Bortho,leftσxyccr, and the compensated right output signal according to Bx,right≈Bsens,right−Bortho,rightσxyccr to determine.

[0082] The compensated differential output signal can then be used according to Bdiff=Bx,left−Bx,right be determined.

[0083] Fig. Figure 5A shows a differential sensor circuit 500A according to another embodiment of the present disclosure. Here too, B x can be determined differentially.

[0084] The differential sensor circuit 500A comprises a first left-hand bridge circuit 310-L. The first left-hand bridge circuit 310-L includes a plurality of first magnetoresistive resistors 312 with a first reference magnetization along a first directional axis (here: x-axis). The first left-hand bridge circuit 310-L also includes an output for a first left-hand output signal V. sens,leftin response to an external magnetic field. In the example shown, the first left bridge circuit 310-L is implemented as a Wheatstone bridge with four first magnetoresistives 312. Ideally (e.g., without voltage), the reference magnetization of the magnetoresistives 312 of the left arm points in the negative x-direction. Ideally, the reference magnetization of the magnetoresistives 312 of the right arm points in the positive x-direction. The first left bridge circuit 310-L can optionally include an offset trim component to correct any inherent offsets in the sensor output and to ensure that the output is exactly centered around zero when no external magnetic field is present. In the example shown, the first left bridge circuit 310-L is configured to measure an x-component of an external magnetic field and produces an output voltage v. sens,left The output voltage V sens,leftThis can be a voltage difference between the center nodes of the left and right legs of the first left-hand bridge circuit 310-L. The person skilled in the art, benefiting from the present disclosure, will understand that the first left-hand bridge circuit 310-L could also be implemented as a half-bridge.

[0085] The differential sensor circuit 500A additionally includes a first right-hand bridge circuit 310-R, which is arranged in close proximity to, but separated by a small distance from, the first left-hand bridge circuit 310-L. The first right-hand bridge circuit 310-R comprises a plurality of first magnetoresistive resistors 312 with a first reference magnetization along a first directional axis (here: x-axis). The first right-hand bridge circuit 310-R also includes an output for a first right-hand output signal V. sens,rightin response to the external magnetic field. In the example shown, the first right-hand bridge circuit 310-R is implemented as a Wheatstone bridge with four first magnetoresistives 312. Ideally (e.g., without voltage), the reference magnetization of the magnetoresistives 312 of the left arm points in the negative x-direction. Ideally, the reference magnetization of the magnetoresistives 312 of the right arm points in the positive x-direction. The first right-hand bridge circuit 310-R can optionally include an offset trim component to correct any inherent offsets in the sensor output and to ensure that the output is precisely centered around zero when no external magnetic field is present. In the example shown, the first right-hand bridge circuit 310-R is configured to measure an x-component of an external magnetic field and produces an output voltage V. sens,right The output voltage V sens,rightThis can be a voltage difference between the center nodes of the left and right legs of the first right-hand bridge circuit 310-R. The person skilled in the art, benefiting from the present disclosure, will understand that the first right-hand bridge circuit 310-R could also be implemented as a half-bridge.

[0086] The differential sensor circuit 500A additionally includes a second bridge circuit 320 (which can be assigned to the first left bridge circuit 310-L and / or the first right bridge circuit 310-R). The second bridge circuit 320 includes a plurality of second magnetoresistives 322 with a second reference magnetization along a second directional axis (here: y-axis). The second bridge circuit 320 also includes an output for a second output signal V. orthoin response to the external magnetic field. In the example shown, the second bridge circuit 320 is implemented as a Wheatstone bridge with four first magnetoresistives 322. Ideally (e.g., without voltage), the reference magnetization of the magnetoresistives 322 of the left arm points in the positive y-direction. Ideally, the reference magnetization of the magnetoresistives 322 of the right arm points in the negative y-direction. The second bridge circuit 320 can optionally include an offset trim component to correct any inherent offsets in the sensor output and to ensure that the output is precisely centered around zero when no external magnetic field is present. In the example shown, the second bridge circuit 320 is configured to measure a y-component of the external magnetic field and produces an output voltage V. ortho The output voltage V orthoThis can be a voltage difference between the center nodes of the left and right legs of the second bridge circuit 320-L. The person skilled in the art, benefiting from the present disclosure, will understand that the second bridge circuit 320 could also be implemented as a half-bridge.

[0087] The differential sensor circuit 500A further comprises a sensor 330 configured to measure a physical quantity indicating a reference magnetization rotation θ of the first magnetoresistives 312 and the second magnetoresistives 322. The physical quantity measured by the sensor 330 can be mechanical stress, temperature, or any other factor that influences the orientation of the reference magnetization in the magnetoresistives 312 and 322.

[0088] The processing circuit arrangement 340 of the differential sensor circuit 500A can be configured to produce an uncompensated differential output signal according to Bsens,diff=Bsens,left−Bsens,right, and the compensated differential output signal according to Bx,diff=Bsens,diff−2BorthoScr to determine.

[0089] Fig. Figure 5B shows a differential sensor circuit 500B according to another embodiment of the present disclosure. Here too, B x can be determined differentially.

[0090] Compared to Fig. The differential sensor circuit 500B (5A) comprises only a first bridge circuit 310. The first bridge circuit 310 in Fig. 5A comprises an upper left magnetoresistance 312, a lower left magnetoresistance 312, an upper right magnetoresistance 312, and a lower right magnetoresistance 312. The left and right magnetoresistances are positioned in close proximity but separated by a distance sufficient for differential measurements. The reference magnetization of the upper left and lower left magnetoresistances 312 points in the positive x-direction. The reference magnetization of the upper right and lower right magnetoresistances 312 also points in the positive x-direction. The upper left and lower right magnetoresistances 312 are connected in series between the supply potential and ground (first series connection). The upper right and lower left magnetoresistances 312 are connected in series between the supply potential and ground (second series connection).The output voltage V. out For example, there could be a voltage difference between the node between the upper left magnetoresistance 312 and the lower right magnetoresistance 312 and the node between the upper right magnetoresistance 312 and the lower left magnetoresistance 312.

[0091] Fig. 5C shows an alternative setup for the second bridge circuit 320.

[0092] The second bridge circuit 320 of Fig. 5C includes an upper left magnetoresistive 322 (G L || G R ), a lower left (insensitive) resistor 2G0, an upper right (insensitive) resistor 2G0 and a lower right magnetoresistance 322 (G L || G RThe reference magnetization of the upper left magnetoresistance 322 and the lower left magnetoresistance 322 points in the positive y-direction. The upper left magnetoresistance 322 and the lower left (insensitive) resistor 2G0 are connected in series between the supply potential and ground (first series connection). The upper right (insensitive) resistor 2G0 and the lower right magnetoresistance 322 (G L || G R ) connected in series between supply potential and ground (second series connection). The output voltage V ortho can be a voltage difference between the center node of the first series circuit and the second series circuit of the alternative second bridge circuit 320.

[0093] Fig. Figure 6 shows an angle sensor circuit 600 according to an embodiment of the present disclosure. An angle sensor typically measures the cosine (cos) and sine (sin) components of a magnetic field to determine the angle of the magnetic field vector relative to a reference axis. This method can be commonly used in angle sensors based on magnetic field detection, such as those using Hall effect sensors, TMR (tunnel magneto-resistance) sensors, or AMR (anisotropic magneto-resistance) sensors.

[0094] Here, the first bridge circuit 310 can measure the cosine component of the angle (cos θ), and the second bridge circuit 320 can measure the sine component of the angle (sin θ). In the illustrated embodiment, the processing circuit arrangement 340 of the angle sensor circuit 600 is configured to generate a first compensated output signal (cos out) based on a difference between the first output signal V and the second bridge circuit 320. horfrom the first bridge circuit 310 and the second output signal V vert from the second bridge circuit 310, scaled on the basis of the measured physical quantity of sensor 330. That is, the processing circuit arrangement 340 can be configured to determine the first compensated output signal based on Bx≈Bhor−BvertScr, or Bx≈Bhor−Bvertσxyccr to determine.

[0095] A second compensated output signal (sin out) is calculated based on a sum of the second output signal V. vert and the first output signal V hor "Scale based on the measured physical quantity of sensor 330, determined. That is, the processing circuit arrangement 340 can be configured to generate the second compensated output signal based on..." By≈Bvert+BhorScr, or By≈Bvert+Bhorσxyccr to determine.

[0096] Additionally or alternatively, a second-order compensation of B can be used. x based on Bx≈Bhor(1−scr22)−BvertScr or Bx≈Bhor(1−σxy2ccr22)−Bvertσxyccr be carried out.

[0097] A second-order compensation of B y can be based on By≈Bvert(1−scr22)−BhorScr, or By≈Bvert(1−σxy2ccr22)−Bhortσxyccr be carried out.

[0098] A corresponding angle sensor circuit 700 with second-order compensation according to an exemplary embodiment is in Fig. 7 shown.

[0099] The processing circuit arrangement 340 of the angle sensor circuit 700 can thus be configured to provide the first compensated output signal B x based on a difference between the first output signal B hor , which uses a first scaling factor based on a squared cross-sensitivity (e.g. (1−Scr22) or (1−σxy2ccr22)) is scaled, and the second output signal B vert , which is scaled with a second scaling factor based on the cross-sensitivity. The processing circuit arrangement 340 can be configured to determine the second compensated output signal B. y based on a sum of the second output signal B vert , which is scaled by the first scaling factor (e.g. (1−Scr22) or (1−σxy2ccr22)), and the first output signal B hor , which is scaled with the second scaling factor.

[0100] The present disclosure proposes a sensor circuit and a method for compensating mechanical stress in magnetoresistive (xMR) sensors. One problem addressed is that xMR sensors, including AMR, GMR, TMR, and CMR sensors, can suffer from stress dependency problems. These problems can lead to changes in sensitivity and reference system rotation, and cause stray field suppression issues in velocity and current sensors, as well as orthogonality errors in angle sensors.

[0101] The proposed solution comprises a sensor circuit including a first and a second bridge circuit with magnetoresistives oriented along orthogonal axes to measure external magnetic fields. The circuit includes a sensor for measuring physical quantities indicating a reference magnetization rotation caused by mechanical stress or other factors. An analog or digital processing circuit determines a compensated output signal based on the first and second output signals and the measured physical quantity.

[0102] The bridge circuits can be configured as Wheatstone bridges, with the first bridge measuring the x-component and the second measuring the y-component of the magnetic field. The sensor can measure physical quantities such as mechanical stress or temperature to indicate the reference magnetization rotation. The analog or digital processing circuitry calculates compensated output signals to correct errors caused by stress-induced magnetization rotation.

[0103] The advantages of this approach include improved accuracy and reliability of xMR sensors through compensation of voltage effects. This can lead to improved measurement accuracy in applications requiring high precision, such as sensors in the automotive industry and industrial equipment.

[0104] Implementation variations include the use of differential measurement techniques and compensation algorithms to reduce the influence of common-mode noise and other disturbances. Different circuit designs and compensation methods include first-order and second-order compensation.

[0105] The aspects and features described in connection with one of the previous examples can also be combined with one or more of the further examples to replace an identical or similar feature of that further example or to additionally introduce the features into the further example.

[0106] Examples may also include or refer to a (computer) program comprising program code for executing one or more of the preceding procedures, if the program is executed on a computer, processor, or other programmable hardware component. Steps, operations, or processes of various procedures described above may therefore also be executed by programmed computers, processors, or other programmable hardware components. Examples may also include program storage devices, such as digital data storage media, that are machine-, processor-, or computer-readable and / or encode and / or comprise machine-executable, processor-executable, or computer-executable programs and instructions. The program storage devices may, for example,Digital storage devices, magnetic storage media such as magnetic disks and tapes, hard disk drives, or optically readable digital data storage media. Further examples may include computers, processors, control units, field-programmable logic arrays ((F)PLAs), field-programmable gate arrays ((F)PGAs), graphics processing units (GPUs), application-specific integrated circuits (ASICs), integrated circuits (ICs), or system-on-a-chip (SoC) systems programmed to perform the steps of the procedures described above.

[0107] It is further understood that the disclosure of several steps, processes, operations, or functions in the description or claims should not be interpreted as necessarily occurring in the described sequence, unless explicitly stated in a specific case or required for technical reasons. Therefore, the preceding description does not restrict the execution of several steps or functions to a specific sequence. Furthermore, in other examples, a single step, function, process, or operation may comprise and / or be broken down into several sub-steps, functions, processes, or operations.

[0108] If certain aspects related to a device or system have been described, these aspects should also be understood as a description of the corresponding procedure. For example, a block, device, or functional aspect of the device or system may correspond to a feature, such as a process step, of the corresponding procedure. Similarly, aspects described in connection with a procedure should also be understood as a description of a corresponding block, element, property, or functional feature of a corresponding device or system.

[0109] The following claims are hereby included in the detailed description, each claim being a separate example. It should also be noted that, although a dependent claim may refer to a specific combination with one or more other claims, other examples may include a combination of the dependent claim with the subject matter of any other dependent or independent claim. Such combinations are hereby explicitly proposed unless it is stated in a specific case that a particular combination is not intended. Furthermore, features of a claim for any other independent claim are also intended to be included, even if that claim is not directly defined as dependent on that other independent claim.

Claims

[1] A sensor circuit (300; 400; 500; 600; 700), comprising a first bridge circuit (310), comprising a plurality of first magnetoresistives (312) with a first reference magnetization along a first directional axis, and an output (314) for a first output signal in response to an external magnetic field; a second bridge circuit (320), comprising a plurality of second magnetoresistives (322) with a second reference magnetization along a second directional axis, and an output (324) for a second output signal in response to the external magnetic field; a sensor (330) configured to measure a physical quantity indicating a reference magnetization rotation of the first and second magnetoresistance (312; 322); and a processing circuit arrangement (340) configured to determine a compensated output signal based on the first output signal, the second output signal and the physical quantity indicating the reference magnetization rotation. [2] The sensor circuit (300; 400; 500; 600; 700) according to claim 1, wherein the first reference magnetization and the second reference magnetization are orthogonal when no external disturbances act on the sensor circuit (300). [3] The sensor circuit (300; 400; 500; 600; 700) according to one of the preceding claims, wherein the first bridge circuit (310) comprises a first Wheatstone bridge comprising four first magnetoresistives, and the second bridge circuit (320) comprises a second Wheatstone bridge comprising four second magnetoresistives. [4] The sensor circuit (300; 400; 500; 600; 700) according to one of the preceding claims, wherein the first output signal is a voltage difference between center nodes of the first bridge circuit (310) and the second output signal is a voltage difference between center nodes of the second bridge circuit (320). [5] The sensor circuit (300; 400; 500; 600; 700) according to one of the preceding claims, wherein the sensor (330) is configured to measure a mechanical stress acting on the sensor circuit (300) as the physical quantity indicating the reference magnetization rotation. [6] The sensor circuit (300; 400; 500; 600; 700) according to one of the preceding claims, wherein the sensor (330) is configured to measure a temperature acting on the sensor circuit (300) as the physical quantity indicating the reference magnetization rotation. [7] The sensor circuit (300; 400; 500; 600; 700) according to one of the preceding claims, wherein the processing circuit arrangement (340) is configured to scale the measured physical quantity by a predetermined scaling factor. [8] The sensor circuit (300; 400; 500; 600; 700) according to one of the preceding claims, wherein the processing circuit arrangement (340) is configured to determine the compensated output signal on the basis of a difference between the first output signal and the second output signal, scaled on the basis of the measured physical quantity. [9] The sensor circuit (300; 400; 500; 600; 700) according to one of the preceding claims, wherein the processing circuit arrangement (340) is configured to to determine a first compensated output signal based on a difference between the first output signal and the second output signal, scaled based on the measured physical quantity, and to determine a second compensated output signal based on a sum of the second output signal and the first output signal, scaled based on the measured physical quantity. [10] The sensor circuit (300; 400; 500; 600; 700) according to one of the preceding claims, wherein the processing circuit arrangement (340) is configured to determine a first compensated output signal based on a difference between the first output signal, scaled by a first scaling factor based on a squared cross-sensitivity, and the second output signal, scaled by a second scaling factor based on the cross-sensitivity, and to determine a second compensated output signal based on a sum of the second output signal, scaled by the first scaling factor, and the first output signal, scaled by the second scaling factor. [11] The sensor circuit (300; 400; 500; 600; 700) according to one of the preceding claims, further comprising a third bridge circuit (310-R), comprising a plurality of third magnetoresistives with the first reference magnetization in the first direction, and an output for a third output signal in response to the external magnetic field, wherein the first and third bridge circuits form a differential sensor; and wherein the processing circuit arrangement (340) is configured to determine the compensated output signal based on the first to third output signals and the physical quantity indicating the cross-sensitivity. [12] The sensor circuit (300; 400; 500; 600; 700) according to claim 11, wherein the processing circuit arrangement (340) is configured to determine the compensated output signal based on a difference between the first and third output signals and the second output signal, scaled on the basis of the measured physical quantity. [13] The sensor circuit (300; 400; 500; 600; 700) according to any one of the preceding claims, wherein the magnetoresistives are tunnel magnetoresistives [14] The sensor circuit (300; 400; 500; 600; 700) according to any one of the preceding claims, wherein the sensor circuit (300) is an integrated circuit. [15] A method for compensating the mechanical stress of a magnetoresistive sensor (300; 400; 500; 600; 700), the method comprising Receiving a first output signal from one or more first magnetoresistives (312) with a first reference magnetization in a first direction in response to an external magnetic field; Receiving a second output signal from one or more second magnetoresistives (322) with a second reference magnetization in a second direction in response to the external magnetic field; Receiving an additional sensor signal indicating a reference magnetization rotation of the first and second magnetoresistives (312; 322); and Determining a compensated output signal based on the first output signal, the second output signal, and the additional sensor signal. [16] The method according to claim 15, comprising determining the compensated output signal based on a difference between the first output signal and the second output signal, scaled on the basis of the additional sensor signal. [17] The method according to claim 15 or 16, comprising Determining a first compensated output signal based on a difference between the first output signal and the second output signal, scaled based on the additional sensor signal, and Determining a second compensated output signal based on a sum of the second output signal and the first output signal, scaled based on the additional sensor signal. [18] The method according to any one of claims 15 to 17, comprising Determining a first compensated output signal based on a difference between the first output signal, scaled by a first scaling factor based on the squared cross-sensitivity, and the second output signal, scaled by a second scaling factor based on the cross-sensitivity, and Determining a second compensated output signal based on a sum of the second output signal scaled by the first scaling factor and the first output signal scaled by the second scaling factor. [19] A computer program comprising a sequence of instructions, wherein the instructions, when executed by a processor, cause the processor to execute the method according to any one of claims 14 to 18.

Images