Sensor circuit and method for compensating for mechanical stresses of magnetoresistive sensor

Abstract

The invention relates to a sensor circuit and a method for compensating for mechanical stress of a magnetoresistive sensor. A sensor circuit (300) is provided comprising a first bridge circuit (310) comprising a plurality of first magnetoresistors (312) having a first reference magnetization along a first directional axis, and an output (314) for a first output signal responsive to an external magnetic field. The sensor circuit (300) also includes a second bridge circuit (320) including a plurality of second magnetoresistors (322) having a second reference magnetization along a second directional axis, and an output (324) for a second output signal responsive to the external magnetic field. The sensor circuit (300) also includes a sensor (300) configured to measure a physical quantity indicative of a reference magnetization rotation of the first magnetoresistor and the second magnetoresistor. The sensor circuit (300) further comprises processing circuitry (340) configured to determine a compensated output signal based on the first output signal, the second output signal, and a physical quantity indicative of the reference magnetization rotation.

Description

Technical Field

[0001] This disclosure generally relates to magnetoresistive sensor circuits, and more particularly to concepts for eliminating or reducing one or more stress effects in magnetoresistive sensor circuits. Background Technology

[0002] The stress dependence of xMR sensors can reflect changes in their sensitivity as a reference system and rotation. The "x" in xMR represents the specific type of magnetoresistive effect utilized. Common types of xMR sensors are AMR (Anisotropic Magnetoresistive) sensors, GMR (Giant Magnetoresistive) sensors, TMR (Tunneling Magnetoresistive) sensors, or CMR (Colossal Magnetoresistive) sensors.

[0003] Anisotropic magnetoresistive (AMR) sensors utilize the anisotropic magnetoresistive effect, where resistance varies based on the angle between the direction of current flow and the magnetization within the material. Giant magnetoresistive (GMR) sensors are based on the giant magnetoresistive effect, which involves large variations in resistance due to the alignment of magnetization in alternating ferromagnetic and nonmagnetic layers. Transient magnetoresistive (TMR) sensors utilize the tunneling magnetoresistive effect, where resistance varies due to electron tunneling between ferromagnetic layers separated by insulating barriers. The tunneling probability depends on the relative alignment of magnetization in the ferromagnetic layers. Colossal magnetoresistive (CMR) sensors rely on the colossal magnetoresistive effect observed in some manganese oxide compounds, where resistance changes significantly in response to an applied magnetic field.

[0004] In the case of xMR sensors, sensitivity refers to the sensor's ability to detect changes in a magnetic field. It is a measurement 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 an xMR sensor. This can cause changes in sensitivity, meaning the sensor may respond more or less to changes in the magnetic field. For example, stress may cause changes in the sensor's resistance, affecting the output signal used for a given magnetic input.

[0005] In xMR sensors, the reference system typically refers to a fixed magnetic layer that provides a stable reference orientation for measuring the relative angle of a free magnetic layer that rotates freely in response to an external magnetic field. Mechanical stress can physically deform the sensor, causing misalignment of the magnetic layer. This deformation can cause the reference magnetic layer to rotate or shift from its intended orientation. This rotation affects the accuracy of sensor measurements because the reference orientation is no longer stable and reliable. This can introduce errors in the measurement of the direction and amplitude of the external magnetic field.

[0006] This stress dependence can cause problems with stray field suppression in speed and current sensors and orthogonality errors in angle sensors. This refers to the sensor's ability to ignore or filter out unwanted magnetic fields (spurious fields) that do not originate from the target signal source. Effective stray field suppression is necessary for accurate measurements in magnetic sensing applications. For example, despite the differential concept used for stray field suppression, in the worst case, up to 25% of the stray field in the orthogonal direction can enter the signal path. Sensitivity mismatch at different locations on the die, up to 10-15%, in the sensitive direction can also lead to poor stray field suppression and prevent speed sensors from working with wheels where the signal spacing is much larger than the sensor spacing.

[0007] Therefore, it may be necessary to eliminate or reduce one or more xMR stress effects. Summary of the Invention

[0008] This need is addressed by the apparatus and method according to the appended claims.

[0009] According to a first aspect, this disclosure provides a sensor circuit. The sensor circuit includes a first bridge circuit. The first bridge circuit (half-bridge or full-bridge) includes a plurality of first magnetoresistives having a first reference magnetization along a first direction axis. The first bridge circuit includes an output for responding to a first output signal in response to an external magnetic field. The sensor circuit includes a second bridge circuit. The second bridge circuit (half-bridge or full-bridge) includes a plurality of second magnetoresistives having a second reference magnetization along a second direction axis. The second bridge circuit includes an output for responding to a second output signal in response to the (same) external magnetic field. The sensor circuit includes a sensor configured to measure a physical quantity indicating rotation of the reference magnetization of the first or second magnetoresistives. The rotation of the reference magnetization may be caused by mechanical stress or other environmental factors. The sensor circuit also includes processing circuitry configured to determine a compensation output signal based on the first output signal, the second output signal, and the measured physical quantity indicating the rotation of the reference magnetization. This compensation is intended to correct for the effects of the rotation of the reference magnetization.

[0010] The advantages of this sensor circuit design can be improved accuracy and reliability. By measuring the physical quantity indicating the rotation of the reference magnetization and using that quantity to compensate for the output signal from the bridge circuit, the sensor can correct for errors caused by mechanical stress or other factors that would otherwise lead to inaccurate readings. This compensation ensures that the sensor provides more accurate and stable measurements, even under changing environmental conditions, enhancing its performance in applications requiring high accuracy, such as automotive sensors, industrial equipment, and consumer electronics.

[0011] In some embodiments, the first and second reference magnetizations are orthogonal in the absence of external perturbations (e.g., mechanical stress) acting on the sensor circuitry. The first reference magnetization refers to the magnetization direction in the first set of magnetoresistive elements in the absence of any external perturbations. The second reference magnetization refers to the magnetization direction in the second set of magnetoresistive elements in the absence of any external perturbations. Ideally, in an undisturbed state, the first and second reference magnetizations can be perpendicular (90 degrees) to each other. Factors such as mechanical stress or other environmental influences may alter / rotate the reference magnetizations. When these perturbations are absent, the reference magnetizations can be orthogonal. The advantage of having orthogonal reference magnetizations in the absence of external perturbations can be improved sensitivity and accuracy in the detected magnetic field. Orthogonal magnetization allows the sensor to more effectively detect and distinguish changes in the magnetic field along different axes. This orthogonal arrangement can maximize the sensor's response to changes in the magnetic field. When external perturbations such as mechanical stress are present, they can cause the reference magnetizations to rotate. Knowing that the initial states are orthogonal allows the processing circuitry to more accurately calculate and apply necessary compensations, correct for any deviations caused by stress, and ensure that the sensor output remains accurate. Orthogonal magnetization can help reduce cross sensitivity between two axes, meaning that changes in the magnetic field along one axis have minimal impact on sensor readings along the other axis.

[0012] In some embodiments, the first bridge circuit includes a first Wheatstone bridge with four first magnetoresistive elements, and the second bridge circuit includes a second Wheatstone bridge with four second magnetoresistive elements. A Wheatstone bridge typically includes four resistors arranged in a diamond shape. It may have two inputs for a voltage source and two outputs where a differential voltage is measured. In this case, the resistors are magnetoresistive elements whose resistance changes in response to an external magnetic field. The differential voltage output from the bridge is a measurement of the magnetic field. An advantage of using a Wheatstone bridge configuration for both the first and second bridge circuits is high sensitivity and accuracy in detecting small changes in the magnetic field. When a magnetoresistive element experiences a change in the external magnetic field, the corresponding resistance change can be detected with high precision. The Wheatstone bridge provides a balanced method for measuring resistance changes. This method can eliminate noise and common-mode signals that could otherwise affect the accuracy of the sensor. The differential output of the bridge can facilitate the measurement of small changes in resistance, making it suitable for precise magnetic field measurements.

[0013] In some embodiments, the first output signal is the voltage difference between the intermediate nodes of the first bridge circuit, and the second output signal is the voltage difference between the intermediate nodes of the second bridge circuit. For a half-bridge configuration, the intermediate nodes are typically two resistors connected to form a single node. The voltage difference can be measured between this intermediate node and a reference point (typically ground or another fixed potential). This provides a simpler yet still effective measurement of resistance changes due to magnetic fields. For a full-bridge configuration, the intermediate nodes are points where resistor pairs are connected. In a full bridge, there are typically two such nodes. The voltage difference between these two intermediate nodes will be used as the output signal. This differential output provides a measurement of resistance changes due to external magnetic fields.

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

[0015] In some embodiments, the sensor is configured to measure the temperature acting on the sensor circuitry as a physical quantity indicating rotation of the reference magnetization. By measuring the temperature, the sensor can infer the degree of magnetization rotation due to thermal effects and apply compensation to maintain accuracy. Temperature changes can cause thermal expansion or contraction of materials, resulting in subsequent changes in mechanical stress and the reference magnetization direction of the magnetoresistor. Measuring the temperature can help determine how much the magnetization has rotated due to thermal effects. Several methods exist for measuring temperature in sensor circuitry, 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 using a predetermined scaling factor. This means that the sensor circuitry may include processing circuitry that adjusts the measured physical quantity (such as stress or temperature) by multiplying it by a specific scaling factor. This scaling factor, also known as a cross-sensitivity coefficient, can be used to calibrate the effect of the physical quantity on the rotation of the sensor's reference magnetization. The processing circuitry can acquire the measured physical quantity (e.g., mechanical stress or temperature) and multiply it by a predetermined scaling factor. This can be a scaling factor used to quantify the relationship between the physical quantity and its effect on the rotation of the reference magnetization. It essentially 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 to accurately correct for deviations caused by stress or temperature variations. 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 a compensated output signal based on the difference between a first output signal and a second output signal scaled based on a measured physical quantity. The first output signal is generated by a first bridge circuit in response to an external magnetic field. The second output signal is generated by a second bridge circuit in response to the same external magnetic field. The measured physical quantity can be a measurement of mechanical stress, temperature, or other factors affecting the reference magnetization of the sensor and its output signal. The second output signal can be scaled by the measured physical quantity. This means that the second output signal can be adjusted based on the measured stress or temperature by a predetermined scaling factor (cross-sensitivity coefficient). The processing circuitry calculates the difference between the first output signal and the scaled second output signal. This difference now incorporates the effect of the measured physical quantity on the second output signal, thereby generating a compensated output signal that takes into account external influences (e.g., along the x-axis B). x (Magnetic field component). This method can improve the accuracy and reliability of the sensor by providing precise compensation for environmental impacts, resulting in consistent and robust performance.

[0018] In some embodiments, the processing circuitry is configured to determine a first compensated output signal based on the difference between a first output signal and a second output signal scaled based on a 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 based on the measured physical quantity. The first compensated output signal (e.g., along the x-axis B) x The magnetic field component can be determined by obtaining 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., along the y-axis B)y The magnetic field components can be determined by summing a second output signal with a first output signal, where the first output signal is scaled based on the measured physical quantity. This method allows for independent compensation of magnetic field components along different axes, resulting in more accurate and reliable multiaxial magnetic field measurements.

[0019] In some embodiments, the processing circuitry is configured to determine a first compensated output signal based on the difference between a first output signal and a second output signal, wherein the first output signal is scaled using a first scaling factor based on squared cross sensitivity, the second output signal is scaled using a second scaling factor based on cross sensitivity, and the processing circuitry is configured to determine a second compensated output signal based on the sum of the second output signal scaled using the first scaling factor and the first output signal scaled using the second scaling factor. This can describe the output signal B used to calculate the compensation. x and B y The method takes into account the cross-sensitivity effect in xMR sensors. The first output signal can be represented along an axis (e.g., horizontal or B). hor The magnetic field measurement is performed along an orthogonal axis (e.g., vertical or B). The second output signal can represent the magnetic field along an orthogonal axis (e.g., vertical or B). vert Magnetic field measurement. Cross sensitivity (S) cr This can refer to the undesirable effect of the magnetic field of one axis on the measurement of another axis due to mechanical stress or other factors. To determine the first compensated output signal (B... x ), the first output signal (e.g., B) hor ) can be used with a factor based on squared cross sensitivity (e.g., (1-S) cr 2 / 2)) scaling. Second output signal (e.g., B) vert It can be used based on cross-sensitivity S cr Factor scaling. First compensated output signal B x It can even be determined by obtaining the difference between the two scaled signals. To determine the second compensated output signal (B)... y ), the second output signal (e.g., B) vert ) can be used with a factor based on squared cross sensitivity (e.g., (1-S) cr 2 / 2)) scaling. First output signal (e.g., B) hor It can be used based on cross-sensitivity S cr Factor scaling. First compensated output signal B x It can even be determined by obtaining the sum between these two scaled signals. This can lead to accurate compensation for the effects of cross-sensitivity, resulting in enhanced measurement accuracy and reliability.

[0020] In some embodiments, the sensor circuitry further includes a third bridge circuit. The third bridge circuitry includes a plurality of third magnetoresistives having a first reference magnetization along a first direction axis. The third bridge circuitry includes an output for a third output signal in response to an external magnetic field. The first and third bridge circuits form a differential sensor. Processing circuitry is configured to determine a compensated output signal based on the first to third output signals and a physical quantity indicating rotation of the reference magnetization. This describes an advanced sensor configuration for improving measurement accuracy and compensation. The first and third bridge circuits can be used together to form a differential sensor. The differential sensor uses two measurements (from the first and third bridge circuits) to enhance the accuracy and robustness of the output signal by eliminating common-mode noise and errors. By using a differential sensor configuration (first and third bridge circuits), the sensor can eliminate common-mode noise and environmental interference that equally affect both circuits. This can result in more accurate and reliable measurements. Processing circuitry combines the output signals from all three bridge circuits (first, second, and third bridge circuits) and uses a measured physical quantity (indicating rotation of the reference magnetization, such as mechanical stress or temperature) to determine the compensated output signal. The compensation output signal is calculated using the first, second, and third output signals, and adjusted based on the measured physical quantity indicating the degree of reference magnetization rotation. This configuration improves measurement accuracy and reduces noise, ensuring reliable and accurate sensor performance under various environmental conditions.

[0021] In some embodiments, the processing circuitry is configured to determine a compensated output signal based on the difference between a first output signal and a third output signal, and a second output signal scaled based on a measured physical quantity. This means the sensor circuitry includes three bridge circuits. The first bridge circuit includes a magnetoresistor having a reference magnetization along a first direction axis and outputs a first signal in response to an external magnetic field. The second bridge circuit includes a magnetoresistor having a reference magnetization along a second (generally orthogonal) direction axis and outputs a second signal in response to an external magnetic field. The third bridge circuit includes a magnetoresistor having a reference magnetization along the first direction axis. The processing circuitry calculates the difference between the first and third output signals. This difference helps reduce common-mode noise and errors, enhancing measurement accuracy. The second output signal is scaled based on a measured physical quantity (such as stress or temperature) to compensate for the effect of that physical quantity on the sensor's reference magnetization. The compensated output signal can be derived by combining the differential signal (the difference between the first and third output signals) and the scaled second output signal. This method ensures that compensation takes into account the measured physical quantity, providing a more accurate and reliable sensor output. The advantage of this method is enhanced compensation for environmental influences and improved accuracy. By using the difference between the first and third output signals, the sensor can effectively eliminate common-mode noise and environmental interference that equally affect both circuits. This results in more accurate and stable measurements. Scaling the second output signal based on the measured physical quantity allows for precise compensation for errors caused by mechanical stress, temperature variations, or other environmental factors, ensuring that the sensor output remains accurate under various conditions.

[0022] In some embodiments, the magnetoresistor is a tunneling magnetoresistor. TMR resistors utilize the tunneling magnetoresistive effect, which occurs when electrons tunnel through an insulating layer between two ferromagnetic layers, where the resistance varies depending on the relative alignment of the magnetization in these layers. A TMR resistor comprises two ferromagnetic layers separated by a thin insulating barrier layer. When a voltage is applied, electrons tunnel through the insulating barrier layer, and the resistance of the device varies depending on whether the magnetization of the ferromagnetic layers is parallel or antiparallel. The resistance is lower when the magnetization is parallel and higher when the magnetization is antiparallel. The advantages of using TMR resistors are high sensitivity and a large magnetoresistance ratio. Compared to other types of magnetoresistors, such as anisotropic magnetoresistors (AMD) or giant magnetoresistors (GMR), TMR resistors typically have a much larger magnetoresistance ratio. This means they can detect smaller changes in magnetic fields with greater accuracy. The high sensitivity of TMR resistors allows for more accurate detection of magnetic fields, which is crucial in applications requiring precise measurements, such as in hard disk drives, magnetic field sensors, and various types of sensing applications in the automotive and industrial sectors.

[0023] In some embodiments, the sensor circuitry is an integrated circuit. This means that the sensor circuitry, including magnetoresistive and processing circuitry, can be fabricated as a single integrated circuit (IC) rather than composed of separate discrete components. An integrated circuit is a group of electronic components, such as resistors, capacitors, transistors, and other devices, all fabricated on a single sheet of semiconductor material (typically silicon). This allows for the creation of compact, efficient, and high-performance electronic systems.

[0024] According to another aspect, this disclosure provides a method for compensating mechanical stress in a magnetoresistor. The method includes: receiving a first output signal from one or more first magnetoresistors, the one or more first magnetoresistors having a first reference magnetization along a first direction axis (e.g., the x-axis), in response to an external magnetic field. The method includes: receiving a second output signal from one or more second magnetoresistors, the second magnetoresistors having a second reference magnetization along a second direction axis (e.g., the y-axis), in response to an external magnetic field. The method includes: receiving an additional sensor signal indicating rotation of the reference magnetization of the first and second magnetoresistors. The method further includes: determining a compensation 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 a compensated output signal based on the difference between a first output signal and a second output signal scaled based on an additional sensor signal.

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

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

[0028] According to another aspect, this disclosure provides a computer program including a sequence of instructions, wherein when executed by a processor, the instructions cause the processor to perform a method of any of the preceding examples.

[0029] This disclosure proposes a scheme to locally eliminate xMR stress effects by compensating for sensitivity loss and reference angle rotation using linear compensation that can be implemented in analog or digital circuitry. Shear stress can be measured directly using a rotating current mirror or indirectly under strong temperature dependence. Attached Figure Description

[0030] The following are some examples of apparatuses and / or methods described by way of example and with reference to the accompanying drawings, wherein:

[0031] Figure 1 A schematic representation of the layer stacking of magnetoresistive sensor elements;

[0032] Figure 2 The diagram illustrates the relationship between cross sensitivity and reference system rotation in a magnetic sensor system.

[0033] Figure 3A A sensor circuit according to an embodiment of the present disclosure is shown;

[0034] Figure 3B A sensor circuit according to another embodiment of the present disclosure is shown;

[0035] Figure 4 A differential sensor circuit according to an embodiment of the present disclosure is shown;

[0036] Figure 5A A differential sensor circuit according to another embodiment of the present disclosure is shown;

[0037] Figure 5B A differential sensor circuit according to another embodiment of the present disclosure is shown;

[0038] Figure 5C The alternative configurations for the second bridge circuit are shown;

[0039] Figure 6 An angle sensor circuit with first-order compensation according to an embodiment of the present disclosure is shown; and

[0040] Figure 7 An angle sensor circuit with second-order compensation according to an embodiment of the present disclosure is shown. Detailed Implementation

[0041] Some examples are described in more detail with reference to the accompanying drawings. However, other possible examples do not limit the features of these embodiments described in detail. Other examples may include modifications to features, as well as equivalents and alternatives to features. Furthermore, the terminology used herein to describe certain examples should not limit other possible examples.

[0042] Throughout the description of the accompanying drawings, the same or similar reference numerals refer to the same or similar elements and / or features, which may be implemented in the same or modified form while providing the same or similar function. For clarity, the thickness of lines, layers, and / or areas in the drawings may also be enlarged.

[0043] When the "or" sign is used to combine two elements A and B, it is understood to disclose all possible combinations: A only, B only, and A and B, unless otherwise explicitly defined in a separate case. As alternative phrases for the same combination, "at least one of A and B" or "A and / or B" may be used. This is equivalent to combinations of more than two elements.

[0044] If the singular forms, such as “a,” “an,” and “the,” are used and the use of a single element is not explicitly or implicitly defined as mandatory, other examples may use several elements to achieve the same functionality. If the functionality described below is implemented using multiple elements, other examples may use a single element or a single processing entity to achieve the same functionality. It should also be understood that the terms “include,” “including,” “comprise,” and / or “comprising,” when used, describe the presence of a particular feature, integer, step, operation, process, element, component, and / or group thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, processes, elements, components, and / or groups thereof.

[0045] Figure 1 An example of a layer stack of magnetoresistive sensor elements 100 according to one or more embodiments is shown.

[0046] The magnetoresistive sensor element 100 can be, for example, a TMR sensor element with a bottom-pinned spin-valve (BSV) configuration. A GMR sensor element is also possible. The magnetoresistive sensor element 100 can be disposed on a semiconductor substrate (not shown) of a magnetoresistive sensor. In a description using a Cartesian coordinate system with mutually perpendicular coordinate axes x, y, and z, the stacked layers extend laterally in the xy-plane spanned by the x and y axes. Therefore, lateral dimensions (e.g., lateral distance, lateral cross-sectional area, lateral surface, lateral extension, lateral displacement, 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 extension of the layer in the z-direction can be referred to as the layer thickness.

[0047] The layer stack of the magnetoresistive sensor element 100 includes at least one reference layer having 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 the sensor axis of the magnetoresistive sensor element 100. The reference layer and therefore the reference magnetization define a sensor plane. The sensor plane may be defined, for example, by an xy plane. Therefore, the x and y directions may be referred to as “in-plane” with respect to the sensor plane, and the z direction may be referred to as “out-of-plane” with respect to the sensor plane.

[0048] Therefore, in the case of GMR or TMR sensor elements, the resistance of the magnetoresistive sensor element 100 is minimum when the free magnetization of the magnetic free layer is exactly in the same direction as the reference magnetization (e.g., the reference direction), and the resistance of the magnetoresistive sensor element 100 is maximum when the free magnetization of the magnetic free layer is exactly in the opposite direction to the reference magnetization. The alignment of the free magnetization of the magnetic free layer is variable in the presence of an external magnetic field. Therefore, the resistance of the magnetoresistive sensor element 100 can vary based on the effect of the external magnetic field on the free magnetization of the free layer.

[0049] From bottom to top, the magnetoresistive sensor element 100 may include an optional seed layer 102, which can be used to influence and / or optimize stack growth. In some embodiments, the seed layer 102 may be composed of copper (Cu), tantalum (Ta), ruthenium (Ru), or combinations 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 may be composed of platinum-manganese (PtMn), iridium-manganese (IrMn), nickel-manganese (NiMn), etc. The thickness of the NAF may, for example, range from 5 nm to 50 nm.

[0050] Furthermore, a pinning layer (PL) 106 may be formed or otherwise arranged on the NAF layer 104. The pinning layer 106 may be composed of a ferromagnetic material, such as cobalt-iron (CoFe) or cobalt-iron-boron (CoFeB). The contact between the NAF layer 104 and the pinning layer 106 can induce an effect called the exchange bias effect, causing the magnetization of the pinning layer 106 to be aligned in a preferred direction (e.g., in the x-direction, as shown). The magnetization of the pinning layer 106 may be referred to as pinning magnetization. The pinning layer 106 may exhibit a permanently fixed linear magnetization pattern (e.g., uniform alignment in one direction) in the xy-plane.

[0051] The magnetoresistive sensor element 100 also includes a nonmagnetic layer (NML), referred to as the coupling interlayer 108. In one possible embodiment, the coupling interlayer 108 may comprise ruthenium (Ru), iridium (Ir), copper (Cu), a copper alloy, or a similar material. Other materials (e.g., paramagnetic materials) are also possible. A magnetic (e.g., ferromagnetic) reference layer (RL) 110 may be formed or otherwise arranged on the coupling interlayer 108. The thicknesses of the pinning layer 106 and the magnetic reference layer 110 may, for example, range from 1 nm to 10 nm.

[0052] Therefore, a coupling interlayer 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 interlayer 108 can provide interlayer exchange coupling (e.g., antiferromagnetic Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling) between the pinned layer 106 and the magnetic reference layer 110 to form an artificial antiferromagnet. Thus, the magnetization of the magnetic reference layer 110 can be aligned and maintained in a direction 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 reference magnetization.

[0053] Since the NAF layer 104 is configured to align and fix the magnetization of the pinned layer 106 in a certain direction, and the coupling interlayer 108 is configured to align and fix the magnetization of the magnetic reference layer 110 in the opposite direction, it can be said that the NAF layer 104 is configured to maintain the magnetization of the pinned layer 106 (e.g., fixed magnetization) in a first magnetic orientation and maintain the magnetization of the magnetic reference layer 110 (e.g., fixed reference magnetization) in a second magnetic orientation. When the pinned layer 106 exhibits a linear magnetization pattern in the antiparallel direction, the magnetic reference layer 110 can exhibit a linear magnetization pattern in a specific direction in the xy plane. Therefore, the NAF layer 104, the pinned layer 106, the coupling interlayer 108, and the magnetic reference layer 110 form the magnetic reference layer system 112 of the magnetoresistive sensor element 100.

[0054] The magnetoresistive sensor element 100 additionally includes a barrier layer 114 (e.g., a tunneling barrier) vertically disposed between the reference layer system 112 and the free magnetic layer 116. The barrier layer 114 may be formed or otherwise disposed on the magnetic reference layer 110 of the reference layer system 112, and the free magnetic layer 116 may be formed or otherwise disposed on the barrier layer 114.

[0055] The barrier layer 114 may be composed of a non-magnetic material. In some embodiments, the barrier layer 114 may be an electrically insulating tunnel barrier layer. For example, the barrier layer 114 may be a tunnel barrier layer for generating the TMR effect. The barrier layer 114 may be composed of magnesium oxide (MgO) or other materials with similar properties.

[0056] The material of the free magnetic layer 116 can be an alloy of ferromagnetic materials, such as CoFe, CoFeB, or NiFe. The free magnetic layer 116 has a variable free magnetization in the presence of an external magnetic field. Therefore, the free magnetic layer 116 can be referred to as a sensor layer because changes in the free magnetization can be used to determine the measured variable. Furthermore, the free magnetization has a standard magnetic orientation (such as vortex magnetization) in the ground state. The ground state is the state in which the effect of the external magnetic field on the free magnetic layer 116 is absent or negligible. In some embodiments, the magnetoresistive sensor element 100 may include a free magnetic system comprising multiple layers (e.g., two or more free magnetic layers) that together serve as a free magnetic layer. In this case, the free magnetic layers of the free magnetic system are magnetically coupled to each other. Therefore, the free magnetic system can serve as a free magnetic layer but also consists of several layers. The free magnetic system has a free magnetization, wherein the free magnetization is variable in the presence of an external magnetic field.

[0057] The capping layer 118, such as tantalum (Ta), tantalum nitride (TaN), ruthenium (Ru), titanium (Ti), titanium nitride (TiN), platinum (Pt), etc., can be formed or otherwise arranged on the free magnetic layer 116 to form the upper layer of the magnetoresistive sensor element 100.

[0058] Seed layer 102 can be used as a bottom electrode or to establish an electrical contact with the bottom electrode (not shown) of magnetoresistive sensor element 100. Capping layer 118 can establish an electrical contact with the top electrode (not shown) of magnetoresistive sensor element 100. Barrier layer 114 can be designed such that when a bias is applied to the electrodes (not shown) of magnetoresistive sensor element 100 to generate a magnetoresistive effect (e.g., TMR effect), electrons can tunnel between reference layer system 112 and free magnetic layer 116.

[0059] As mentioned above, Figure 1 This is an example used only as a magnetoresistive sensor element or magnetoresistor. Other examples may differ. Figure 1 The description in [the text]. Figure 1 The number and arrangement of components shown are illustrative. In practice, magnetor 100 may include additional elements or layers.

[0060] Mechanical stress can cause the reference magnetization of magnetic reference layer 110 or reference layer system 112 to rotate compared to its orientation in a stress-free state. Mechanical stress can affect the magnetic properties of a material due to magnetoelastic coupling, an interaction between the magnetic and elastic properties of a material. When a magnetic material is subjected to mechanical stress, the stress can cause changes in the magnetic anisotropy of the material, resulting in a rotation of the reference magnetization direction. Magnetoelastic coupling is an interaction between the magnetic and mechanical properties of a material. Stress can alter the magnetic energy profile of a material, causing changes in the direction of reference magnetization. Mechanical stress can introduce or modify anisotropy in a material. Anisotropy refers to the direction dependence of a material's magnetic properties. Stress can enhance or redirect existing anisotropy, resulting in a rotation of the reference magnetization. In TMR sensors or other magnetoresistive sensors, any rotation of the reference magnetization caused by mechanical stress can lead to errors in the sensor's output because the sensor relies on a stable and well-defined magnetization direction for accurate measurement.

[0061] Figure 2 The diagram illustrates the cross sensitivity S in a magnetic sensor system. cr The relationship between the rotation θ of the reference system and the reference system. Figure 2 The x-axis in the figure represents the cross sensitivity S as a percentage (%). cr . Figure 2 In this equation, the y-axis represents the rotation θ of the reference system in degrees (°). Equation:

[0062]

[0063] Showing the cross sensitivity S cr It is essentially equal to the tangent of the angle θ of the reference system rotation or reference magnetization rotation. The diagonal in Figure 200 indicates the cross sensitivity S. cr The direct proportional relationship between the cross sensitivity S and the reference magnetization rotation θ. As the reference system / magnetization rotation θ increases, the cross sensitivity S... cr It also increases. For example, approximately 20% of the cross-sensitivity S cr This corresponds to a reference system / magnetization rotation of approximately 11°.

[0064] exist Figure 2 The illustration in the lower right corner visually represents the reference system rotated by an angle θ. The original axes (x and y) represent the original reference (coordinate) system. The axes (x' and y') represent the reference system that has rotated, for example, due to mechanical stress.

[0065] A rotating reference system can cause misalignment between the actual magnetic field direction and the direction sensed 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 it was previously less sensitive to (increasing cross-sensitivity). This increased cross-sensitivity can introduce noise and errors into measurements, especially in multi-axis sensors. Furthermore, rotation can cause interference between orthogonal axes (e.g., the x and y axes), making it difficult to accurately isolate magnetic field components.

[0066] This disclosure proposes a compensation concept that takes into account a rotating reference system and can help correct measurements. For example, the proposed compensation concept uses a known relationship between cross sensitivity and reference angle rotation (see example...). Figure 2 Use this to adjust the reading.

[0067] Figure 3A A sensor circuit 300 according to an embodiment of the present disclosure is shown.

[0068] Sensor circuit 300 includes a first bridge circuit 310. The first bridge circuit 310 includes a plurality of first magnetoresistives 312 having a first reference magnetization along a first direction axis (here, the x-axis). The first bridge circuit 310 also includes a first output signal V in response to an external magnetic field. sens The output is 314. In the illustrated example, the first bridge circuit 310 is implemented as a Wheatstone bridge with four first magnetoresistive elements 312. Ideally (e.g., in the absence of stress), the reference magnetization of the magnetoresistive element 312 in the left branch points towards the negative x-axis. Ideally, the reference magnetization of the magnetoresistive element 312 in the right branch points towards the positive x-axis (i.e., shifted 180° relative to the left branch). The first bridge circuit 310 may optionally include offset fine-tuning components to correct the sensor output V. sens Any inherent offset, ensuring that the output V is constant when no external magnetic field is present. sens Accurately centered at zero. In the illustrated example, the first bridge circuit 310 is configured to measure the x-component of the external magnetic field and generate an output voltage V. sens Output voltage V sens It can be the voltage difference between the intermediate nodes of the left and right branches of the first bridge circuit 310. Those skilled in the art who benefit from this disclosure will understand that the first bridge circuit 310 can also be implemented as a half-bridge.

[0069] The first bridge circuit 310 includes an upper left magnetoresistor 312, a lower left magnetoresistor 312, an upper right magnetoresistor 312, and a lower right magnetoresistor 312. The reference magnetization of the upper left and lower left magnetoresistors 312 points in the negative x-direction. The reference magnetization of the upper right and lower right magnetoresistors 312 points in the positive x-direction. The upper left and lower right magnetoresistors 312 are connected in series between the power supply potential and ground (first series connection). The upper right and lower left magnetoresistors 312 are connected in series between the power supply potential and ground (second series connection). Output voltage V sens It can be the voltage difference between the intermediate nodes of the first series connection and the second series connection of the first bridge circuit 310.

[0070] The sensor circuit 300 additionally includes a second bridge circuit 320. The second bridge circuit 320 includes a plurality of second magnetoresistives 322 having a second reference magnetization along a second direction axis (here, the y-axis). The second bridge circuit 320 also includes a second output signal V in response to an external magnetic field. ortho The output is 324. In the illustrated example, the second bridge circuit 320 is implemented as a Wheatstone bridge with four second magnetoresistive elements 322. Ideally (e.g., in the absence of stress), the reference magnetization of the magnetoresistive element 322 in the left branch points towards the positive y-axis. Ideally, the reference magnetization of the magnetoresistive element 322 in the right branch points towards the negative y-axis (i.e., shifted 180° relative to the left branch). The second bridge circuit 320 may optionally include offset fine-tuning components to correct the sensor output V. ortho Any inherent offset, ensuring that the output V is constant when no external magnetic field is present. ortho Accurately centered at zero. In the illustrated example, the second bridge circuit 320 is configured to measure the y-component of the external magnetic field and generate an output voltage V. ortho Output voltage V ortho It can be the voltage difference between the intermediate nodes of the left and right branches of the second bridge circuit 320. Those skilled in the art who benefit from this disclosure will understand that the second bridge circuit 320 can also be implemented as a half-bridge.

[0071] The second bridge circuit 320 includes an upper left magnetoresistor 322, a lower left magnetoresistor 322, an upper right magnetoresistor 322, and a lower right magnetoresistor 322. The reference magnetization of the upper left and lower left magnetoresistors 322 points in the positive y-direction. The reference magnetization of the upper right and lower right magnetoresistors 322 points in the negative y-direction. The upper left and lower right magnetoresistors 322 are connected in series between the power supply potential and ground (first series connection). The upper right and lower left magnetoresistors 322 are connected in series between the power supply potential and ground (second series connection). Output voltage V ortho It can be the voltage difference between the intermediate nodes of the first and second series connections in the second bridge circuit 320.

[0072] The sensor circuit 300 also includes a sensor 330 configured to measure a physical quantity 334 indicating a reference system / magnetization rotation θ of the first magnetoresistor 312 and the second magnetoresistor 322. The physical quantity 334 measured by the sensor 330 can be mechanical stress, temperature, or any other factor affecting the orientation of the reference magnetization in the magnetoresistors 312, 322. The measured physical quantity can help determine how much the reference system / magnetization has rotated due to external influences.

[0073] In some embodiments, all components of the sensor circuit 300 may be implemented on a common substrate, such as a common semiconductor substrate (die). That is, the sensor circuit 300 may be an integrated sensor circuit (sensor IC).

[0074] In one implementation ( Figure 3A The sensor 330 can be configured to measure the mechanical (shear) stress acting on the sensor circuit 300 as a physical quantity indicating a change in reference magnetization, which manifests itself as a rotation θ in the reference magnetization direction, thereby causing a cross sensitivity S of the field orthogonal to the magnetization direction. cr .

[0075] Mechanical stress can be measured using various techniques and specialized circuitry designed for detecting and quantifying stress. For example, the piezoresistive effect utilizes the change in resistance of a material under mechanical stress. The resistance of a typical resistor bar changes according to applied stress, which can be measured and used to quantify the stress. Utilizing the piezoelectric-MOS effect, mechanical stress alters the mobility of charge carriers in the channel of a MOSFET, affecting current gain and threshold voltage. These changes can be measured to determine stress. The piezoelectric-junction effect involves changes in the mobility of minority carriers and intrinsic carrier density in the base of a bipolar transistor, thus affecting the saturation current. Stress can be measured by observing these changes. Utilizing the piezoelectric-Hall effect, mechanical stress alters the Hall coefficient, which changes the current-dependent magnetic sensitivity of the Hall plate. Measuring changes in Hall sensitivity can indicate the stress level.

[0076] For example, sensor 330 may include a MOS current mirror having current flow directions in orthogonal directions, which can be used as a stress-sensitive element. An advantage is that the signal is in the current domain, making it simple to multiplex an array of elements onto a single terminal. A combination of low-n-doped lateral resistors (lateral resistors) and low-n-doped vertical resistors (vertical resistors) in an L-layout can be used to measure stress. The difference in resistance change of these resistors under stress can be used to quantify the stress. Four resistors in an L-layout can form a Wheatstone bridge circuit. The difference between the bridge's output voltage and the in-plane normal stress component (σ) is used to quantify the stress. xx -σyy This is proportional to the stress, thus allowing for the measurement of stress.

[0077] In another embodiment of sensor circuit 300 ( Figure 3B Sensor 330 can be configured to measure the temperature acting on sensor circuit 300 as a physical quantity indicating mechanical (shear) stress and thus indicating the rotation of the reference magnetization. By measuring the temperature, sensor 330 can infer the degree of magnetization rotation due to thermal effects and apply compensation to maintain accuracy. Temperature changes can cause thermal expansion or contraction of materials, resulting in changes in mechanical stress and the reference magnetization direction of the subsequent magnetoresistor. Measuring the temperature can help determine how much the magnetization has rotated due to thermal effects. Several methods exist for measuring temperature in sensor circuits, including thermocouples, thermistors, RTDs (resistance temperature detectors), or semiconductor temperature sensors. For example, stress measurements can also be used to obtain temperature measurements and conversions from the measurement data (like S). cr (T) = (T-150) / (190)*0.2) is used instead. The remaining cross-sensitivity is expected to be at approximately ±3% and can be further reduced by fine-tuning the sample at 150°: S cr (T) = (T-150) / (190)*0.2 + fine-tuning.

[0078] Temperature and / or stress sensors can be placed near circuit elements 310, 320 to measure the temperature and / or stress acting on circuit elements 310, 320 and provide input to a compensation circuit that corrects for drift caused by stress.

[0079] The sensor circuit 300 also includes a processing circuit (compensation circuit) 340, which is configured to process the first output signal V. sens Second output signal V ortho The compensation output signal 344 is determined by the physical quantity 334 indicating the reference system / magnetization rotation θ. Compensation can be performed based on the following relationship:

[0080]

[0081] Among them B sens Corresponding to the first output signal, B ortho Corresponding to the second output signal, B x Corresponding to the first output signal of the compensation, and B y The second output signal corresponds to the compensation.

[0082] That is, based on the first output signal B sens Second output signal B ortho The first output signal B of the compensation x It can be determined according to the following formula:

[0083] B x =B sens cosθ-B ortho sinθ

[0084] B x ≈B sens -B ortho θ=B sens -B ortho tan(S cr ),,

[0085] B x ≈B sens -B ortho S cr ,

[0086] B x ≈B sens -B ortho σ xy c cr .

[0087] This equation represents a linear approximation, where B x It is the compensated magnetic field component in the x-direction. B x The quadrature voltage output B can be subtracted from the main voltage output. ortho and cross sensitivity S cr It is calculated by multiplying the products.

[0088] Based on the first output signal B sens Second output signal B ortho The second output signal B of the compensation y It can be determined according to the following formula:

[0089] B y =B sens sinθ+B ortho cosθ,

[0090] B y ≈B sens θ+B ortho =B sens tan(S cr )+B ortho ,,

[0091] B y ≈B sens S cr +B ortho ,

[0092] B y ≈B sens σ xy c cr +B ortho .

[0093] This equation represents a linear approximation, where B y It is the compensated magnetic field component in the y-direction. B y By adjusting the voltage output B sens Multiply by cross sensitivity S cr and quadrature voltage output B ortho The calculation is done by summing.

[0094] Here, θ = atan(S) cr ) indicates reference magnetization rotation, S cr =σ xy c cr This represents the cross sensitivity, and c cr =For example, 0.3% / MPa represents the cross sensitivity coefficient. For example, shear stress σ xy Temperature-dependent LUT values ​​can be used for measurement or fine-tuning. Therefore, the processing circuit device 340 can be configured to operate using a predetermined scaling factor c. cr (Cross sensitivity coefficient) to further analyze the indicated (shear) stress σ xy The measured physical quantity is scaled. The cross sensitivity coefficient depends on the material. The cross sensitivity coefficient refers to the sensitivity of a sensor or material to unexpected stimuli (such as mechanical stress), which can cause deviations from the sensor's intended measurement. Different materials can have varying stiffness, which affects how they deform under stress. Materials with higher elastic modulus generally exhibit lower deformation, affecting cross sensitivity. Materials like silicon exhibit a piezoresistive effect, where mechanical stress changes resistance. The magnitude of this effect varies with the material's properties. The atomic arrangement in a material can affect how stress propagates through that material. Single-crystal silicon, for example, has anisotropic properties, meaning it responds to stress changes with direction. In silicon, the level and type of doping (n-type or p-type) can affect the piezoresistive coefficient. Heavily doped silicon can have different stress sensitivities compared to lightly doped silicon. The temperature dependence of the piezoresistive effect means that 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 inherent properties, doping level, temperature effects, and manufacturing process.

[0095] Figure 3A or Figure 3B The processing circuit device 340 can be configured based on the first output signal B sens The second output signal B is scaled based on the measured physical quantity. ortho The difference between them determines the compensated output signal B. x Second output signal B ortho For example, by S cr =σ xy ccr Scaling. Additionally or optionally, the processing circuitry 340 can be configured to scale based on the second output signal B. ortho The first output signal B is scaled based on the measured physical quantity by 334. sens The sum of these factors determines the compensation output signal B. y First output signal B sens For example, by S cr =σ xy c cr Scaling. Material-specific scaling factor c cr (For example, 0.24% / MPa) can be used to quantify the sensor's response to mechanical stress (σ). xy The sensitivity of the parameter in question is 0.24% / MPa. This means that for every megapascal (MPa) of stress applied, the parameter in question (e.g., output voltage) changes by 0.24%.

[0096] Figure 4 A sensor circuit 400 according to another embodiment of the present disclosure is shown. Here, the external magnetic field component B x It can be determined differentially. External magnetic field component B x Differential measurement involves comparing magnetic fields 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 effects of common-mode noise and other external interference. In differential measurement, two magnetic sensors are placed very close to each other, but separated by a small distance. These sensors detect the magnetic field component B at their respective locations. x The outputs of the two sensors are compared to find the difference between them. This differential output effectively measures the change in magnetic field with the distance between the sensors.

[0097] The differential sensor circuit 400 includes a first left bridge circuit 310-L. The first left bridge circuit 310-L includes a plurality of first magnetoresistives 312 having a first reference magnetization along a first direction axis (here: the x-axis). The first left bridge circuit 310-L also includes a first left output signal V in response to an external magnetic field. sens,left The output of the sensor is shown. In the illustrated example, the first left bridge circuit 310-L is implemented as a Wheatstone bridge with four first magnetoresistive elements 312. Ideally (e.g., in the absence of stress), the reference magnetization of the magnetoresistive elements 312 in the left branch points in the negative x-direction. Ideally, the reference magnetization of the magnetoresistive elements 312 in the right branch points in the positive x-direction. The first left bridge circuit 310-L may optionally include offset fine-tuning components to correct any inherent offset in the sensor output, ensuring that the output is accurately centered at zero when no external magnetic field is present. In the illustrated example, the first left bridge circuit 310-L is configured to measure the x-component of an external magnetic field and generate an output voltage V. sens,left Output voltage Vsens,left It can be the voltage difference between the intermediate nodes of the left and right branches of the first left bridge circuit 310-L. Those skilled in the art who benefit from this disclosure will understand that the first left bridge circuit 310-L can also be implemented as a half bridge.

[0098] The differential sensor circuit 400 includes a second left bridge circuit 320-L. The second left bridge circuit 320-L includes a plurality of second magnetoresistives 322 having a second reference magnetization along a second direction axis (here: the y-axis). The second left bridge circuit 320-L also includes a second output signal V in response to an external magnetic field. ortho,left The output of the second left bridge circuit 320-L is shown in the illustrated example. In this example, the second left bridge circuit 320-L is implemented as a Wheatstone bridge with four second magnetoresistive elements 322. Ideally (e.g., in the absence of stress), the reference magnetization of the magnetoresistive elements 322 in the left branch points in the positive y-direction. Ideally, the reference magnetization of the magnetoresistive elements 322 in the right branch points in the negative y-direction. The second left bridge circuit 320-L may optionally include offset fine-tuning components to correct any inherent offset in the sensor output, ensuring that the output is accurately centered at zero when no external magnetic field is present. In the illustrated example, the second left bridge circuit 320-L is configured to measure the y-component of an external magnetic field and generate an output voltage V. ortho,left Output voltage V ortho,left It can be the voltage difference between the intermediate nodes of the left and right branches of the second left bridge circuit 320-L. Those skilled in the art who benefit from this disclosure will understand that the second left bridge circuit 320-L can also be implemented as a half bridge.

[0099] The differential sensor circuit 400 also includes a left sensor 330-L, which is configured to measure a physical quantity 334 indicating a reference magnetization rotation θ of the first left magnetoresistor 312 and the second left magnetoresistor 322. The physical quantity 334 measured by the sensor 330 can be mechanical stress, temperature, or any other factor affecting the orientation of the reference magnetization in the magnetoresistors 312, 322.

[0100] The differential sensor circuit 400 also includes a first right bridge circuit 310-R, which is positioned very close to but at a small distance from the first left bridge circuit 310-L. The first right bridge circuit 310-R includes a plurality of first magnetoresistives 312 having a first reference magnetization along a first direction axis (here: the x-axis). The first right bridge circuit 310-R also includes a first right output signal V in response to an external magnetic field. sens,rightThe output of the first right bridge circuit 310-R is shown in the illustrated example. In this example, the first right bridge circuit 310-R is implemented as a Wheatstone bridge with four first magnetoresistive elements 312. Ideally (e.g., in the absence of stress), the reference magnetization of the magnetoresistive elements 312 in the left branch points in the negative x-direction. Ideally, the reference magnetization of the magnetoresistive elements 312 in the right branch points in the positive x-direction. The first right bridge circuit 310-R may optionally include offset fine-tuning components to correct for any inherent offset in the sensor output, ensuring that the output is accurately centered at zero when no external magnetic field is present. In the illustrated example, the first right bridge circuit 310-R is configured to measure the x-component of an external magnetic field and generate an output voltage V. sens,right Output voltage V sens,right It can be the voltage difference between the intermediate nodes of the left and right branches of the first right bridge circuit 310-R. Those skilled in the art who benefit from this disclosure will understand that the first right bridge circuit 310-R can also be implemented as a half bridge.

[0101] The differential sensor circuit 400 additionally includes a second right bridge circuit 320-R, which is positioned very close to but at a small distance from the second left bridge circuit 320-L. The second right bridge circuit 320-R includes a plurality of second magnetoresistives 322 having a second reference magnetization along a second direction axis (here: the y-axis). The second right bridge circuit 320-R also includes a second right output signal V in response to an external magnetic field. ortho,right The output of the second right bridge circuit 320-R is shown in the illustrated example. In this example, the second right bridge circuit 320-R is implemented as a Wheatstone bridge with four second magnetoresistive elements 322. Ideally (e.g., in the absence of stress), the reference magnetization of the magnetoresistive elements 322 in the left branch points in the positive y-direction. Ideally, the reference magnetization of the magnetoresistive elements 322 in the right branch points in the negative y-direction. The second right bridge circuit 320-R may optionally include offset fine-tuning components to correct any inherent offset in the sensor output, ensuring that the output is accurately centered at zero when no external magnetic field is present. In the illustrated example, the second right bridge circuit 320-R is configured to measure the y-component of an external magnetic field and generate an output voltage V. ortho,right Output voltage V ortho,right It can be the voltage difference between the intermediate nodes of the left and right branches of the second right bridge circuit 320-R. Those skilled in the art who benefit from this disclosure will understand that the second right bridge circuit 320-R can also be implemented as a half bridge.

[0102] The differential sensor circuit 400 also includes a right sensor 330-R, which is configured to measure a physical quantity indicating a reference magnetization rotation θ of the first right magnetoresistor 312 and the second right magnetoresistor 322. The physical quantity measured by sensor 330-R can be mechanical stress, temperature, or any other factor affecting the orientation of the reference magnetization in the magnetoresistor.

[0103] The processing circuit 340 of the differential sensor circuit 400 can be configured to determine the compensated left output signal according to the following formula:

[0104] B x,left ≈B sens,left -B ortho,left σ xy c cr ,

[0105] And the compensated right output signal, according to the following formula:

[0106] B x,right ≈B sens,right -B ortho，right σ xy c cr .

[0107] Then, the compensated differential output signal can be determined according to the following formula:

[0108] B diff =B x,left -B x,right .

[0109] Figure 5A A differential sensor circuit 500A according to another embodiment of the present disclosure is shown. Here, B x It can also be determined differentially.

[0110] The differential sensor circuit 500A includes a first left bridge circuit 310-L. The first left bridge circuit 310-L includes a plurality of first magnetoresistives 312 having a first reference magnetization along a first direction axis (here: the x-axis). The first left bridge circuit 310-L also includes a first left output signal V in response to an external magnetic field. sens,left The output of the sensor is shown. In the illustrated example, the first left bridge circuit 310-L is implemented as a Wheatstone bridge with four first magnetoresistive elements 312. Ideally (e.g., in the absence of stress), the reference magnetization of the magnetoresistive elements 312 in the left branch points in the negative x-direction. Ideally, the reference magnetization of the magnetoresistive elements 312 in the right branch points in the positive x-direction. The first left bridge circuit 310-L may optionally include offset fine-tuning components to correct any inherent offset in the sensor output, ensuring that the output is accurately centered at zero when no external magnetic field is present. In the illustrated example, the first left bridge circuit 310-L is configured to measure the x-component of an external magnetic field and generate an output voltage V. sens,left Output voltage V sens,left It can be the voltage difference between the intermediate nodes of the left and right branches of the first left bridge circuit 310-L. Those skilled in the art who benefit from this disclosure will understand that the first left bridge circuit 310-L can also be implemented as a half bridge.

[0111] The differential sensor circuit 500A additionally includes a first right bridge circuit 310-R, which is positioned very close to but at a small distance from the first left bridge circuit 310-L. The first right bridge circuit 310-R includes a plurality of first magnetoresistives 312 having a first reference magnetization along a first direction axis (here: the x-axis). The first right bridge circuit 310-R also includes a first right output signal V in response to an external magnetic field. sens,right The output of the first right bridge circuit 310-R is shown in the illustrated example. In this example, the first right bridge circuit 310-R is implemented as a Wheatstone bridge with four first magnetoresistive elements 312. Ideally (e.g., in the absence of stress), the reference magnetization of the magnetoresistive elements 312 in the left branch points in the negative x-direction. Ideally, the reference magnetization of the magnetoresistive elements 312 in the right branch points in the positive x-direction. The first right bridge circuit 310-R may optionally include offset fine-tuning components to correct for any inherent offset in the sensor output, ensuring that the output is accurately centered at zero when no external magnetic field is present. In the illustrated example, the first right bridge circuit 310-R is configured to measure the x-component of an external magnetic field and generate an output voltage V. sens,right Output voltage V sens,right It can be the voltage difference between the intermediate nodes of the left and right branches of the first right bridge circuit 310-R. Those skilled in the art who benefit from this disclosure will understand that the first right bridge circuit 310-R can also be implemented as a half bridge.

[0112] The differential sensor circuit 500A additionally includes a second bridge circuit 320 (which may be associated with 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 having a second reference magnetization along a second direction axis (here: the y-axis). The second bridge circuit 320 also includes a second output signal V in response to an external magnetic field. ortho The output of the second bridge circuit 320 is shown in the illustrated example. In this example, the second bridge circuit 320 is implemented as a Wheatstone bridge with four second magnetoresistive elements 322. Ideally (e.g., in the absence of stress), the reference magnetization of the magnetoresistive element 322 in the left branch points in the positive y-direction. Ideally, the reference magnetization of the magnetoresistive element 322 in the right branch points in the negative y-direction. The second bridge circuit 320 may optionally include offset fine-tuning components to correct for any inherent offset in the sensor output, ensuring that the output is accurately centered at zero when no external magnetic field is present. In the illustrated example, the second bridge circuit 320 is configured to measure the y-component of an external magnetic field and generate an output voltage V. ortho Output voltage V ortho It can be the voltage difference between the intermediate nodes of the left and right branches of the second left bridge circuit 320-L. Those skilled in the art who benefit from this disclosure will understand that the second bridge circuit 320 can also be implemented as a half bridge.

[0113] The differential sensor circuit 500A also includes a sensor 330 configured to measure a physical quantity indicating a reference magnetization rotation θ of the first magnetoresistor 312 and the second magnetoresistor 322. The physical quantity measured by the sensor 330 may be mechanical stress, temperature, or any other factor affecting the orientation of the reference magnetization in the magnetoresistors 312, 322.

[0114] The processing circuit 340 of the differential sensor circuit 500A can be configured to determine the uncompensated differential output signal according to the following formula:

[0115] B sens,diff =B sens,left -B sens,right ,

[0116] And the output signal of the differential compensation, according to the following formula:

[0117] B x,diff =B sens,diff -2B ortho S cr .

[0118] Figure 5B A differential sensor circuit 500B according to another embodiment of the present disclosure is shown. Here, B x It can also be determined differentially.

[0119] and Figure 5A In contrast, the differential sensor circuit 500B only includes a first bridge circuit 310. Figure 5A The first bridge circuit 310 includes an upper left magnetoresistor 312, a lower left magnetoresistor 312, an upper right magnetoresistor 312, and a lower right magnetoresistor 312. The left and right magnetoresistors are placed very close but spaced sufficiently apart for differential measurement. The reference magnetization of the upper left and lower left magnetoresistors 312 points in the positive x-direction. The reference magnetization of the upper right and lower right magnetoresistors 312 also points in the positive x-direction. The upper left and lower right magnetoresistors 312 are connected in series between the power supply potential and ground (first series connection). The upper right and lower left magnetoresistors 312 are connected in series between the power supply potential and ground (second series connection). For example, the output voltage V out It can be the voltage difference between the node between the upper left magnetor 312 and the lower right magnetor 312 and the node between the upper right magnetor 312 and the lower left magnetor 312.

[0120] Figure 5C An alternative configuration of the second bridge circuit 320 is shown.

[0121] Figure 5C The second bridge circuit 320 includes the upper left magnetor 322 (G L ||GR ), lower left (insensitive) resistor 2G0, upper right (insensitive) resistor 2G0 and lower right magnetoresistor 322 (G L ||G R The reference magnetization of the upper left magnetor 322 and the lower right magnetor 322 points in the positive y-direction. The upper left magnetor 322 and the lower left (insensitive) resistor 2G0 are connected in series between the power supply potential and ground (first series connection). The upper right (insensitive) resistor 2G0 and the lower right magnetor 322 (G... L ||G R It is connected in series between the power supply potential and ground (second series connection). Output voltage V ortho It could be the voltage difference between the intermediate nodes of the first and second series connections of the alternative second bridge circuit 320.

[0122] Figure 6 An angle sensor circuit 600 according to an embodiment of the present disclosure is shown. Angle sensors typically measure the cosine and sinine components of a magnetic field to determine the angle of the magnetic field vector relative to a reference axis. This method can generally be used in angle sensors based on magnetic field sensing, such as angle sensors using Hall effect sensors, TMR (tunneling magnetoresistive) sensors, or AMR (anisotropic magnetoresistive) sensors.

[0123] Here, the first bridge circuit 310 can measure the cosine component (cosθ) of the angle, and the second bridge circuit 320 can measure the sine component (sinθ) of the angle. In the illustrated example, the processing circuitry 340 of the angle sensor circuit 600 is configured to measure the first output signal V from the first bridge circuit 310. hor With the second output signal V from the second bridge circuit 310 vert The difference between them determines the first compensated output signal (cos out) and the second output signal V. vert The physical quantity measured from sensor 330 is scaled. That is, the processing circuitry 340 can be configured to determine the first compensated output signal based on the following formula:

[0124] B x ≈B hor -B vert S cr ,or

[0125] B x ≈B hor -B vert σ xy c cr .

[0126] The second compensated output signal (sin out) is based on the second output signal V. vertThe first output signal V is scaled based on the physical quantity measured from sensor 330. hor The sum is determined. That is, the processing circuit device 340 can be configured to determine the second compensated output signal based on the following formula:

[0127] B y ≈B vert +B hor S cr ,or

[0128] B y ≈B vert +B hor σ xy c cr .

[0129] Additionally or optionally, B x The second-order compensation can be based on the following formula:

[0130] or

[0131]

[0132] B y The second-order compensation can be based on the following formula:

[0133] or

[0134]

[0135] exist Figure 7 The diagram shows an angle sensor circuit 700 with second-order compensation according to an embodiment.

[0136] Therefore, the processing circuit device 340 of the angle sensor circuit 700 can be configured based on the first output signal B. hor With the second output signal B vert The difference between them determines the first compensated output signal B. x First output signal B hor Use a first scaling factor based on squared cross sensitivity (e.g., or Scaling, second output signal B vert Scaling is performed using a second scaling factor based on cross-sensitivity. The processing circuitry 340 can be configured to scale based on a first scaling factor (e.g., ...). or ) Scaling of the second output signal B vert The first output signal B scaled by the second scaling factor hor The sum of the two signals determines the second compensated output signal B. y .

[0137] This disclosure presents a sensor circuit and method for compensating for mechanical stress in magnetoresistive (xMR) sensors. The problem addressed is the stress dependence that can exist in xMR sensors, including AMR, GMR, TMR, and CMR sensors. These problems can lead to variations in sensitivity and reference system rotation, causing stray field suppression issues in velocity and current sensors and orthogonality errors in angle sensors.

[0138] The proposed solution involves a sensor circuit comprising a first bridge circuit and a second bridge circuit, each having a magnetoresistor oriented along an orthogonal axis to measure an external magnetic field. The circuit includes a sensor that measures a physical quantity indicating a rotation of a reference magnetization caused by mechanical stress or other factors. Analog or digital processing circuitry determines a compensated output signal based on a first output signal, a second output signal, and the measured physical quantity.

[0139] The bridge circuit can be configured as a Wheatstone bridge, where a first bridge measures the x-component of the magnetic field and a second bridge measures the y-component. Sensors can measure physical quantities such as mechanical stress or temperature to indicate a rotation of the reference magnetization. Analog or digital processing circuitry calculates a compensated output signal to correct for errors caused by stress-induced magnetization rotation.

[0140] The advantages of this method include improved accuracy and reliability of xMR sensors by compensating for stress effects. This can lead to enhanced measurement accuracy in applications requiring high precision, such as automotive sensors and industrial equipment.

[0141] Variations in implementation involve the use of differential measurement techniques and compensation algorithms to reduce the effects of common-mode noise and other interference. Various circuit embodiments and compensation methods include first-order and second-order compensation.

[0142] The aspects and features described in a particular example from the previous examples can also be combined with one or more examples from the sad examples to replace the same or similar features of those other examples or additionally introduce features into other examples.

[0143] Examples may also be or relate to a (computer) program that includes program code, which, when executed on a computer, processor, or other programmable hardware component, performs one or more of the methods described above. Therefore, the steps, operations, or processes of the different methods described above may also be executed by a programmed computer, processor, or other programmable hardware component. Examples may also cover program storage devices, such as digital data storage media, which are machine-readable, processor-readable, or computer-readable and encode and / or contain machine-executable, processor-executable, or computer-executable programs and instructions. For example, a program storage device may include or may be a digital storage device, such as magnetic storage media like disks and tapes, hard disk drives, or optically readable digital data storage media. Other examples may also include computers, processors, control units, (field-programmable logic arrays) ((F)PPLA), (field-programmable gate arrays) ((F)PGA), 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 methods described above.

[0144] It should also be understood that the disclosure of several steps, processes, operations, or functions in the specification or claims should not be construed as implying that these operations must depend on the described order, unless expressly stated in individual cases or necessary for technical reasons. Therefore, the preceding description does not limit the execution of several steps or functions to a particular order. Furthermore, in other examples, a single step, function, process, or operation may include and / or be decomposed into several sub-steps, sub-functions, sub-processes, or sub-operations.

[0145] If aspects of a device or system have already been described, these aspects should also be understood as descriptions of the corresponding methods. For example, a block, device, or functional aspect of a device or system may correspond to a feature of the corresponding method, such as method steps. Therefore, aspects describing a method should also be understood as descriptions of corresponding blocks, elements, properties, or functional characteristics of the corresponding device or system.

[0146] The following claims are hereby incorporated into the detailed description, wherein each claim may be considered an independent example. It should also be noted that although in the claims, dependent claims refer to a particular combination with one or more other claims, other examples may also include combinations of dependent claims with the subject matter of any other dependent or independent claim. Such combinations are expressly stated herein unless it is indicated in individual cases that a particular combination is not desired. Furthermore, the features of a claim should also be included in any other independent claim, 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), including: The first bridge circuit (310) includes: A plurality of first magnetoresistive elements (312) having a first reference magnetization along a first direction axis, and The output (314) is used to respond to the first output signal of the external magnetic field. The second bridge circuit (320) includes: Multiple second magnetoresistive elements (322) having a second reference magnetization along a second direction axis, and The output (324) is used to respond to the second output signal in response to the external magnetic field; Sensor (330) is configured to measure a physical quantity indicating a reference magnetization rotation of the first magnetoresistor (312) and the second magnetoresistor (322); and The processing circuit device (340) is configured to determine a compensation output signal based on the first output signal, the second output signal, and the physical quantity indicating the rotation of the reference magnetization.

2. The sensor circuit (300; 400; 500; 600; 700) according to claim 1, wherein, In the absence of external perturbations acting on the sensor circuit (300), the first reference magnetization and the second reference magnetization are orthogonal.

3. The sensor circuit (300; 400; 500; 600; 700) according to any one of the preceding claims, wherein the first bridge circuit (310) includes a first Wheatstone bridge, the first Wheatstone bridge including four first magnetoresistive elements, and the second bridge circuit (320) includes a second Wheatstone bridge, the second Wheatstone bridge including four second magnetoresistive elements.

4. The sensor circuit (300; 400; 500; 600; 700) according to any one of the preceding claims, wherein the first output signal is the voltage difference between intermediate nodes of the first bridge circuit (310), and the second output signal is the voltage difference between intermediate nodes of the second bridge circuit (320).

5. The sensor circuit (300; 400; 500; 600; 700) according to any one of the preceding claims, wherein the sensor (330) is configured to measure the mechanical stress acting on the sensor circuit (300) as the physical quantity indicating the rotation of the reference magnetization.

6. The sensor circuit (300; 400; 500; 600; 700) according to any one of the preceding claims, wherein the sensor (330) is configured to measure the temperature acting on the sensor circuit (300) as the physical quantity indicating the rotation of the reference magnetization.

7. The sensor circuit (300; 400; 500; 600; 700) according to any one of the preceding claims, wherein the processing circuit device (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 any one of the preceding claims, wherein the processing circuit device (340) is configured to determine the compensated output signal based on the difference between the first output signal and the second output signal scaled based on the measured physical quantity.

9. The sensor circuit (300; 400; 500; 600; 700) according to any one of the preceding claims, wherein the processing circuit device (340) is configured to: The first compensated output signal is determined based on the difference between the first output signal and the second output signal scaled based on the measured physical quantity. The second compensated output signal is determined based on the 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 any one of the preceding claims, wherein the processing circuit device (340) is configured to: A first compensation signal is determined based on the difference between the first output signal and the second output signal. The first output signal is scaled using a first scaling factor based on the squared cross sensitivity, and the second output signal is scaled using a second scaling factor based on the cross sensitivity. The second compensated output signal is determined 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.

11. The sensor circuit (300; 400;) according to any one of the preceding claims 500； 600； 700), also includes: The third bridge circuit (310-R) includes: A plurality of third magnetoresistors, having a first reference magnetization in the first direction, and The output is used in response to the third output signal of the external magnetic field. The first bridge circuit and the third bridge circuit form a differential sensor; and The processing circuit device (340) is configured to determine the compensated output signal based on the first output signal to the third output signal 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 device (340) is configured to determine the compensated output signal based on the difference between the first output signal and the third output signal and the second output signal scaled based on the measured physical quantity.

13. The sensor circuit (300; 400; 500; 600; 700) according to any one of the preceding claims, wherein the magnetoresistor is a tunnel magnetoresistor.

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 mechanical stress in a magnetoresistive sensor (300; 400; 500; 600; 700), the method comprising: In response to an external magnetic field, a first output signal is received from one or more first magnetoresistive devices (312), the one or more first magnetoresistive devices (312) having a first reference magnetization in a first direction; In response to the external magnetic field, a second output signal is received from one or more second magnetoresistive devices (322), the one or more second magnetoresistive devices (322) having a second reference magnetization in a second direction; Receive additional sensor signals indicating the reference magnetization rotation of the first magnetoresistor (312) and the second magnetoresistor (322); as well as The compensation output signal is determined based on the first output signal, the second output signal, and the additional sensor signal.

16. The method of claim 15, comprising: The compensated output signal is determined based on the difference between the first output signal and the second output signal scaled based on the additional sensor signal.

17. The method according to claim 15 or 16, comprising: A first compensated output signal is determined based on the difference between the first output signal and the second output signal scaled based on the additional sensor signal. The second compensated output signal is determined based on the 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: A first compensation signal is determined based on the difference between the first output signal and the second output signal. The first output signal is scaled using a first scaling factor based on the squared cross sensitivity, and the second output signal is scaled using a second scaling factor based on the cross sensitivity. The second compensated output signal is determined 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.

19. A computer program comprising a sequence of instructions, wherein when executed by a processor, the instructions cause the processor to perform the method of any one of claims 14 to 18.

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